Gunter started his career as a striker when he played for local youth sides Durham Colts and Albion Rovers in Newport but switched to playing as a full back at a young age and signed for the Cardiff City youth side at the age of eight. He signed his first professional contract with the club on 1 August 2006 along with fellow Cardiff academy graduate Darcy Blake.

Primarily a right-sided defender, Gunter made his senior debut for Cardiff on 22 August 2006 against Barnet in the League Cup first round, playing the full 90 minutes of a 2–0 loss at Ninian Park. After being included in the first team squad on several occasions, his league debut came in a 1–0 home loss to Queens Park Rangers on 17 November 2006. Gunter was praised for his performance by manager Dave Jones, who commented “Chris did the right things, let nobody down, and will only get stronger.” Gunter would later describe his second league appearance, a 4–1 defeat to Hull City, as one of the lowest points of his career. However, he was able to maintain his place in the squad, competing with Kevin McNaughton and Kerrea Gilbert.

At age 16 years and 299 days, Gunter became the second youngest player to play for the Wales Under-21 team behind Lewin Nyatanga when he played against Cyprus Under-21 in 2006.

In March 2007 he won the Football League’s Apprentice of the Year award after impressing in the first team squad due to injuries to some regular players and during the summer of 2007, Gunter was the subject of two bids of £500,000 and £1 million from Premier League club Everton. Both, however, were rejected. At the end of the 2006–07 season, having made sixteen appearances in all competitions, he became Cardiff’s youngest player to win a senior international cap after making his debut, beating the 48 year old club record held by Graham Moore.

According to reports on 21 December 2007, Cardiff agreed a substantial fee with Tottenham Hotspur and therefore allowed Gunter to enter into talks with the club. Cardiff also stated that Tottenham had “met their valuation of the player” which had previously been reported at £4 million. On 22 December Gunter passed a medical at White Hart Lane with a view to a £2 million move. The move was made official on 24 December and he joined the club after the transfer window opened on 1 January 2008.

Gunter received his first call up to the senior international side at the age of seventeen for a friendly match against New Zealand at the end of his first season of professional football, describing himself as being “absolutely staggered”. He made his debut for Wales in the match on 26 May 2007 at the Racecourse Ground, Wrexham, featuring for the first half of a 2–2 draw. He was ever present at right back during 2010 World Cup qualifying and was the only player in the squad to have played in all ten matches.

Gunter made his debut for Spurs on 15 January in an FA Cup third round tie against Reading at the Madejski Stadium, playing the entirety of a 1–0 victory. Fifteen days later, he made his top-flight debut for Spurs, playing 62 minutes of a goalless draw at Everton before being replaced by Kevin-Prince Boateng. He made only one more league appearance that season, filling in for Didier Zokora for the final 17 minutes of a 4–1 loss at Birmingham City on 1 March. He was cup-tied for their win in the 2008 Football League Cup Final.

His second season did not see him become a regular, as he featured in only three league matches, playing the full 90 minutes in none of them. On 12 March 2009, Gunter moved on loan to Nottingham Forest for the rest of the 2008–09 season.

On 17 July 2009, Tottenham Hotspur accepted a bid of £1.75 million from Nottingham Forest. Forest completed the signing of Gunter on 20 July on a four-year contract. He scored his first goal for the club in a 1–0 victory at Plymouth Argyle on 27 September 2009. It was also Gunter’s first goal in senior football. In the match between Nottingham Forest and Crystal Palace on 23 March 2010, Gunter made his 100th senior club appearance. In May 2010, he was selected in the Championship PFA Team of the Year for the 2009–10 season.

On 15 August 2010, Gunter and Sanchez Watt were booked by referee Tony Bates for an on-field altercation; however later that month the FA retrospectively gave Gunter a three-match ban when replays showed him stamping on the Leeds United player.

On 8 October 2010, Gunter received a straight red card in added time for a professional foul against Dimitar Rangelov in the 0–1 home loss against Bulgaria in a Euro 2012 qualifying match at the Cardiff City Stadium. Aged 24, he won his 50th cap for Wales in the 1–1 away draw with Belgium in 2014 FIFA World Cup qualification on 15 October 2013.

A regular at right-back during his time at Forest, Gunter scored his only other goal for the club on 16 August 2011, the only goal of a match at Doncaster Rovers.

Gunter completed a move to Reading on 17 July 2012, signing a three-year deal for the club who had been promoted to the Premier League. The fee was undisclosed but has been reported to have been between £2.3 million and £2.5 million. He scored his first goal for Reading against Peterborough United in the League Cup on 28 August 2012, the 3–2 home victory putting the team into the third round. He played 20 league matches for the Royals, who ended the season relegated. On 29 November 2013, Gunter was sent off as Reading won 3–2 at his former club Forest.

On 27 March 2015, Reading took up the option in Gunter’s contract to extend his stay with the Royals for an additional year. In the League Cup first round on 11 August, he scored the extra-time only goal as Reading won away at Colchester United.

On 18 February 2016, Gunter signed a new two-year contract to keep him at Reading until the summer of 2018. Gunter again extended his contract with Reading on 5 July 2017, agreeing a new three-year contract, keeping him at the club until the summer of 2020. In October 2017, Gunter was named Welsh Footballer of the Year by the Football Association of Wales.

Gunter was part of Wales’ UEFA Euro 2016 23-man squad and played every minute of their six games as they reached the semi-finals. He won his 75th cap, aged just 27 years, on 6 October 2016 in a 2–2 away draw against Austria in 2018 FIFA World Cup qualifying.

He captained the side for the first time for Wales’ friendly with Panama on 13 November 2017, in which he equalled his former manager Gary Speed’s record of 85 international caps for an outfield player. The following 22 March, Gunter made the record his own when he featured in a 6–0 win over China at the 2018 China Cup. On 20 November 2018, he surpassed Neville Southall’s record of 92 caps for Wales in a 1–0 friendly loss away to Albania, in which he was captain for the second time.

After Gomes’ departure from Reading on 9 October 2019, Gunter and Garath McCleary were recalled to the first team. Both players had been transfer listed and told they would be leaving the club in the previous summer. It was not until 26 November that he made his first appearance of the season, making his 500th career appearance in club football in 1–0 home defeat to Leeds United – also his 225th league start for Reading. On 1 January 2020, profiting from Yiadom’s injury, he made his 300th appearance for Reading in a 2–1 win at Fulham. Gunter was released by Reading in July 2020 at the completion of his contract.

On 8 October 2020, Gunter joined Charlton Athletic on a two-year deal.