Keane was part of the squad that participated in the 1988 UEFA European Under-16 Football Championship although he did not play. He was man of the match for the Republic of Ireland national under-19 team when they beat hosts Hungary in the 1990 UEFA European Under-18 Football Championship to qualify for the 1991 FIFA World Youth Championship.

Initially, Keane was turned down from the Ireland schoolboys squad after a trial in Dublin; one explanation from former Ireland coach and scout Ronan Scally was that the 14-year-old Keane was “just too small” to make it at the required level. Undeterred, he began applying for trials with English clubs, but he was turned down by each one. As his childhood years passed, he took up temporary jobs involving manual work while waiting for a breakthrough in his football prospects. In 1989, he eventually signed for the semi-professional Irish club Cobh Ramblers after persuasion from Ramblers’ youth team manager Eddie O’Rourke. Keane was one of two Ramblers representatives in the inaugural FAI/FAS scheme in Dublin, and it was through this initiative that he got his first taste of full-time training. His rapid progression into a promising footballer was reflected by the fact that he would regularly turn out for Ramblers’ youth side as well as the actual first team, often playing twice in the same weekend as a result.

When called up for his first game at the international level, an under-21s match against Turkey in 1991, Keane took an immediate dislike to the organisation and preparation surrounding the Irish team, later describing the set-up as “a bit of a joke”. He would continue to hold this view throughout the remainder of his time spent with the national team, which led to numerous confrontations with the Irish management. Keane declared his unavailability to travel with the Irish squad to Algeria, but was surprised when manager Jack Charlton told him that he would never play for Ireland again if he refused to join up with his compatriots. Despite this threat, Keane chose to stay at home on the insistence of Nottingham Forest manager Brian Clough, and was pleased when a year later he was called up to the Irish squad for a friendly at Lansdowne Road. After more appearances, he grew to disapprove of Charlton’s style of football, which relied less on the players’ skill and more on continuous pressing and direct play. Tensions between the two men peaked during a pre-season tournament in the United States when Charlton berated Keane for returning home late after a drinking session with Steve Staunton.

Keane was beginning to attract attention from the top clubs in the Premier League, and in 1992, Blackburn Rovers manager Kenny Dalglish spoke to Keane about the possibility of a move to the Lancashire club at the end of the season. With Forest struggling in the league and looking increasingly likely to be relegated, Keane negotiated a new contract with a relegation escape clause. The lengthy negotiations had been much talked about in public, not least by Brian Clough, who described Keane as a “greedy child” due to the high wages demanded by the Irishman. “Keane is the hottest prospect in football right now, but he is not going to bankrupt this club”, Clough stated. Despite the extended contract negotiations, Forest fans voted him the club’s Player of the Season. Despite his best efforts, Keane could not save Forest from relegation, and the clause in his contract became activated. Blackburn agreed a £4 million fee for Keane, who soon after agreed to a contract with the club.

Keane scored 33 league goals for Manchester United and a total of 51 in all competitions. The first two of his goals for the club came in the 3–0 home win over Sheffield United in the Premier League on 18 August 1993, the last on 12 March 2005 in a 4–0 away win over Southampton in the FA Cup.

Keane is married to Theresa Doyle, and they have five children: Shannon, Caragh, Aidan, Leah and Alanna. They married in 1997.

Keane caused controversy in November 2000, when he criticised sections of United supporters after the Champions League victory over Dynamo Kyiv at Old Trafford. He complained about the lack of vocal support given by some fans when Dynamo was dominating the game, stating, “Away from home our fans are fantastic, I’d call them the hardcore fans. But at home, they have a few drinks and probably the prawn sandwiches, and they don’t realise what’s going on out on the pitch. I don’t think some of the people who come to Old Trafford can spell ‘football’, never mind understand it.” Keane’s comments started a debate in England about the changing atmosphere in football grounds, and the term “prawn sandwich brigade” is now part of the English football vocabulary, referring to people who attend football games or claim to be fans of football because it is fashionable rather than due to any genuine interest in the game.

Keane made headlines again in the 2001 Manchester derby, when five minutes from the final whistle, he was sent off for a knee-high foul on Alf-Inge Håland in what was seen by many as an act of revenge. He initially received a three-match suspension and a £5,000 fine from The Football Association (FA), but further punishment was to follow after the release of Keane’s autobiography in August 2002, in which he stated that he intended “to hurt” Håland. Keane’s account of the incident was as follows:

In August 2002, Keane was fined £150,000 by Sir Alex Ferguson and suspended for three matches for elbowing Sunderland’s Jason McAteer, and this was compounded by an added five-match suspension for the controversial comments about Håland. Keane used the break to undergo an operation on his hip, which had caused him to take painkillers for a year beforehand. Despite early fears that the injury was career-threatening, and suggestions of a future hip-replacement from his surgeon, he was back in the United team by December.

Mick McCarthy resigned as Ireland manager in November 2002 after defeats to Russia and Switzerland in qualification for Euro 2004. The possibility of Keane returning to the squad for future qualifiers was raised, as Keane had not yet fully retired from international football, insisting that McCarthy’s presence was the main incentive for staying away from the Irish squad. McCarthy’s replacement, Brian Kerr, discussed with Keane the possibility of a recall, and in April 2004 he was brought back into the Irish team to face Romania on 27 May. Keane was not reinstated as captain, however, as Kerr decided to keep the armband with Kenny Cunningham. After the team’s failure to qualify for the 2006 World Cup, he announced his retirement from international football to help prolong his club career.

Regarding his work-rate, mentality, and influence, his former teammate Gary Neville said of him: “His greatest gift was to create a standard of performance which demanded the very best from the team. You would look at him busting a gut and feel that you’d be betraying him if you didn’t give everything yourself.” Steve McClaren, who served as Alex Ferguson’s assistant manager during Keane’s time at Manchester United, between 1998 and 2001, instead said of the midfielder’s competitive spirit: “He mirrors the manager on the pitch. They are winners.” Regarding Keane’s complex character, despite his intensity on the pitch, Sean O’Hagan of The Guardian wrote in 2002 that he is “…a committed and confident warrior on the field, a shy, socially awkward, and often lonely introvert off it.”

During his period of rest after the operation, Keane reflected on the cause of his frequent injuries and suspensions. He decided that the cause of these problems was his reckless challenges and angry outbursts which had increasingly blighted his career. As a result, he became more restrained on the field and tended to avoid the disputes and confrontations with other players. Some observers felt that the “new” Keane had become less influential in midfield as a consequence of the change in his style of play, possibly brought about by decreased mobility after his hip operation. After his return, however, Keane displayed the tenacity of old, leading the team to another league title in May 2003.

Keane also jointly holds the record for the most red cards received in English football, being dismissed a total of 13 times in his career. He was inducted into the English Football Hall of Fame in 2004 in recognition of his impact on the English game and became the only Irish player to be selected into the FIFA 100, a list of the greatest living footballers picked by Pelé.

Throughout the 2000s, Keane maintained a fierce rivalry with Arsenal captain Patrick Vieira. The most notable incident between the two took place at Highbury in 2005 at the height of an extreme period of bad blood between United and Arsenal. Vieira was seen confronting United defender Gary Neville in the tunnel before the game over his fouling of José Antonio Reyes in the previous encounter between the two sides, prompting Keane to verbally confront the Arsenal captain.

Overall, Keane led United to nine major honours, making him the most successful captain in the club’s history. Keane scored his 50th goal for Manchester United on 5 February 2005 in a league game against Birmingham City. His appearance in the 2005 FA Cup final, which United lost to Arsenal in a penalty shoot-out, was his seventh such game, a record in English football at the time.

Keane unexpectedly left Manchester United by mutual consent on 18 November 2005, during a protracted absence from the team due to an injury sustained in his last competitive game for the club, caused by a robust challenge from Luis García against Liverpool. His departure marked the climax of increasing tensions between Keane and the United management and players since the club’s pre-season training camp in Portugal when he argued with Ferguson over the quality of the set-up at the resort. Ferguson was angered further by Keane’s admission during an MUTV phone-in that he would be “prepared to play elsewhere” after the expiration of his current contract with United at the end of the season.

On 15 December 2005, Keane was announced as a Celtic player, the team he had supported as a child. Initial reports suggested Keane was offered a contract of around £40,000 per week; however, this was rejected by the player himself in his second autobiography, in which he claimed he was only paid £15,000 per week while a Celtic player. Keane’s Celtic career began in January 2006, when the Glasgow giants crashed to a 2–1 defeat to Scottish First Division side Clyde in the third round of the Scottish Cup. His abrasive style had not dwindled, as he was seen criticising some of his new team-mates during the match. Keane scored what turned out to be his only Celtic goal a month later, a shot from 20 yards in a 2–1 Scottish Premier League victory over Falkirk. He retained his place the following Sunday in his first Old Firm derby against Rangers, leading Celtic to victory. Celtic went on to complete a double of the Scottish Premier League title and Scottish League Cup, his last honour as a player.

Keane’s testimonial took place at Old Trafford on 9 May 2006 between United and Celtic. The home side won the game 1–0, with Keane playing the first half for Celtic and the second half in his former role as Manchester United captain. The capacity crowd of 69,591 remains the largest crowd ever for a testimonial match in England. All of the revenue generated from the match was given to Keane’s favourite charity, Irish Guide Dogs for the Blind.

On 12 June 2006, Keane announced his retirement from professional football on medical advice, only six months after joining Celtic. His announcement prompted glowing praise from many of his former colleagues and managers, not least from Sir Alex Ferguson, who opined, “Over the years when they start picking the best teams of all time, he will be in there.”

Following her rise to fame, Triggs was mentioned by several sources on many occasions, with Keane “dogged” by numerous canine references for the remainder of his career. In 2006 when Keane moved house to Sunderland, his reunion with Triggs, who joined him later, came to the notice of the press. In 2007, Keane was reported to have heard of his team’s promotion to the Premiership while walking Triggs. The following year, Keane was said to have acquired a German Shepherd Dog named Izac to accompany Triggs.

Keane has reiterated his displeasure with the attitude and selection policy of the FAI. In March 2007, Keane claimed that several Republic of Ireland players get picked solely based on their media exposure and that the organisation was biased towards players originating from Dublin or other regions of Leinster: “Once you keep playing them on the reputation they’ve built up through the media or because they do lots of interviews, then it’s wrong. There’s a fine line between loyalty and stupidity.” Keane claimed that Sunderland player Liam Miller was not picked because he was from Cork and that players with significant potential were failing to get picked for the national team. He also alleged that the FAI were incompetent in the running of their affairs.

Keane’s first two games as manager could not have gone much better; first coming from behind to beat Derby County 2–1, followed by an easy 3–0 victory over Leeds United. Sunderland began to steadily creep up the league standings under Keane’s management, and by the turn of the year, they had escaped the bottom half of the league. Five further players were signed during the January 2007 transfer window, three (Anthony Stokes, Carlos Edwards and Stern John) on permanent contracts and two (Jonny Evans and Danny Simpson) on loan from Manchester United, Keane’s old club. Results continued to improve, and Keane was rewarded with the February and March Manager of the Month awards, while his team began to challenge for the automatic promotion places. Meanwhile, Keane tackled his players’ non-professional approach with a firm hand. When three players were late for the team coach to a trip to Barnsley, in March 2007, he simply left them behind.

The beginning of the 2008–09 season would prove to be tumultuous. In September 2008 Keane became embroiled in a row with FIFA Vice-President Jack Warner over the withdrawal of Dwight Yorke from the Trinidad and Tobago national team. Warner accused Keane of being disrespectful towards small countries. Keane responded by calling Warner “a clown” and insisted that Yorke was retired from international football. That same month Keane experienced “one of the worst and longest nights” of his career when Sunderland had to come from 2–0 down at home in a League Cup tie against Northampton Town. The game ended 2–2, with Sunderland progressing narrowly on penalties.

Keane was involved in further controversy in the wake of Ireland’s defeat by France in the qualification 2010 World Cup play-off. During an Ipswich Town press conference on 20 November 2009, Keane was critical of the Irish reaction to the Thierry Henry handball incident. His response included criticisms of the Irish team’s defence and the FAI authorities.

In an interview with The Irish Times on 21 February 2009, Keane cited differences with Sunderland 30% shareholder Ellis Short and strains with club chairman Niall Quinn as the factors in his decision to resign as Sunderland manager.

On 23 April 2009, Keane was appointed as the new manager of Ipswich Town on a two-year contract, the day after the club had dismissed Jim Magilton. His first game in charge came the following Saturday with a 3–0 away win over Cardiff City, the final league match to be played at Ninian Park. The following week, Ipswich rounded off the season with a 2–1 win over Coventry City. In the 2009–10 season, Keane started to sign some players, some of them from his former club Sunderland. He signed goalkeeper Márton Fülöp, midfielders Carlos Edwards and Grant Leadbitter and brought in Jack Colback, David Healy and Daryl Murphy on loan to the club. Ipswich started without a win in their first 14 matches, making them the last team to record their first win in the whole league, finally winning on 31 October against Derby County and recording their first away win of the season on 29 November against Cardiff City. Their form gradually improved throughout the season, but Ipswich drew far too many games to come anywhere near the promotion race and they finished the season in 15th place. Many inconsistencies in the 2009–10 and the 2010–11 season meant that Keane’s Ipswich side never really challenged for promotions and as a result of a poor run of form, ending up with his side dropping to as low as 21st in the Championship. Keane was dismissed as Ipswich manager on 7 January 2011.

On 6 June 2009, it was announced that Keane and his family would purchase a house in the Ipswich area, near to the training ground of Keane’s new club, Ipswich Town. He eventually settled in the nearby market town of Woodbridge. They moved out of the property and offered it for sale in 2015.

In later life, Triggs was involved in a police investigation when her behaviour caused an argument between Keane and a neighbour. She appeared in an Irish Guide Dogs advertisement in 2009 – whereupon the Irish Examiner referred to her as “football’s biggest canine celebrity” – and also received her own profile on Facebook. Triggs was described as a “celebrity” and a “household name” upon erroneous reports of her death from cancer in September 2010. Keane was described as “inconsolable”. The Irish Examiner’s obituary noted how “At critical moments when the nation’s happiness seemed entwined with Roy’s moods, he turned to his Labrador Triggs and took to the road”.

Keane had a Labrador Retriever named Triggs, who died in 2012. Speaking in Dublin at his annual visit to the Irish Guide Dogs for the Blind he spoke on the loss affecting him, “Triggs was great and went through a lot with me.. you will have me crying in a minute, so be careful. She had a good life.” Triggs came to international attention in 2002 during an incident ahead of that year’s FIFA World Cup when Keane engaged in a public quarrel and left the squad. The footballer said of Triggs, “Unlike humans, dogs don’t talk shit.”

On 5 November 2013, the FAI announced that Martin O’Neill had been made the Republic of Ireland manager and that Keane had been made the assistant manager. Their first match was against Latvia at the Aviva Stadium in a 3–0 victory on 15 November 2013. After Neil Lennon left Celtic at the end of the 2013–14 season, Keane looked set to become the new manager of the Hoops. Martin O’Neill admitted he won’t stand in his way of taking over the reins at Celtic Park. Keane, however, remained as assistant manager of Ireland and asked not to be considered for the job. Keane later stated that he was on the verge of taking the Celtic job and had met with the Celtic owner Dermot Desmond but felt “they didn’t make him feel wanted enough” and rejected the offer. Keane later became the new assistant manager of Aston Villa, combining his role with Villa and Ireland.

In October 2014, Keane caused controversy after his book was released before crucial Euro 2016 qualifiers against Gibraltar and Germany. Martin O’Neill, however, rejected the claims that it was a distraction.

On 1 July 2014, Keane was confirmed as Aston Villa’s new assistant manager, working alongside manager Paul Lambert. He combined this role with his assistant manager’s role with the Republic of Ireland. On 28 November 2014, however, Keane quit his role as assistant manager at Aston Villa to concentrate on his assistant manager role with Ireland.

In October 2014, Keane released the second part of his autobiography The Second Half, which was ghostwritten by Roddy Doyle. It is the follow up to his first autobiography, released in 2002 which was ghost written by Eamon Dunphy.

In November 2018, Keane and O’Neill left their jobs by “mutual agreement”.

Keane, in an interview with the Irish media company, Off the Ball, in September 2019, stated that Manchester United were pushing to get him out of the club because he was getting old and his strained relationship with then assistant manager Carlos Queiroz and later on with Sir Alex Ferguson, rather than the mere MUTV incident.

In January 2019 he became assistant manager at Nottingham Forest, leaving the role in June 2019.

Later, Keane had a change of heart. Keane along with Harry Redknapp and Gareth Southgate (who Keane was sent off for stamping on during an FA Cup semi-final in 1995) were pundits for ITV’s coverage of the Champions League final between Manchester United and Barcelona. In the 2011–12 season, he became ITV chief football analyst, appearing on nearly every Live ITV match alongside presenter Adrian Chiles and Gareth Southgate. He appeared on ITV in the Champions League including Chelsea’s victory in the final against Bayern Munich, nearly all FA Cup matches including the final between Chelsea and Liverpool at Wembley, and England competitive internationals and friendlies. He was also involved in the ITV team for Euro 2012 alongside longtime rival Patrick Vieira and they appeared together as pundits in Ireland–Spain match and Czech Republic–Russia match, also appearing with Roberto Martínez and Gordon Strachan. Keane joined Sky Sports to work on Super Sunday starting in September 2019.