Born in Dourados, Mato Grosso do Sul, Lucas began his career at Grêmio as a midfielder in 2005. The following year was a successful year for him, as Grêmio won the Rio Grande do Sul state championship (the Campeonato Gaúcho) for the first time since 2001, and also came third in the Campeonato Brasileiro Série A. Lucas also became the youngest player ever to receive Placar magazine’s Bola de Ouro (Golden Ball), given to the best player in the Campeonato Brasileiro – an honour previously won by the likes of Zico, Falcão, Careca, Alex, Romário, Robinho, Kaká and Carlos Tevez.

His form in 2006 led to reported interest from many major European clubs including offers from top Spanish clubs and Internazionale. It was Liverpool that proved most attractive to the player, however, and on 13 May 2007, the club confirmed they had signed the player from Grêmio before the start of the 2007–08 season. The transfer fee was in the region of £6 million.

In October 2006, Lucas was included in the senior Brazilian squad for friendlies against Kuwaiti club Al-Kuwait and Ecuador. Lucas was both the youngest member and one of only two non-Europe based players in a strong squad. He made his debut for Brazil on 7 October 2006 coming on as a second-half substitute against Al-Kuwait. Brazil won the match 4–0, but his appearance did not count as his first cap—the match was not considered an official friendly match by FIFA.

On 26 July 2007, he was officially unveiled as a Liverpool player for a fee of £5 million and was given international clearance to compete in the final of the Barclays Asia Trophy.

Lucas is the former captain of the Brazilian under-20 team. He led the team to victory in the 2007 South American Youth Championship, scoring four goals in the process. He was expected to lead the team again in the 2007 FIFA U-20 World Cup held in Canada in July 2007 and was named in their squad, but an injury in training kept him from playing for three weeks, leading to his withdrawal from the squad.

Lucas gained his first official Brazil international cap on 22 August 2007, coming on as a substitute in a friendly against Algeria. In June 2008, Lucas was named in the Brazil squad for an Olympics warm-up match later in the month.

By late November, manager Rafael Benítez gave Lucas his chance to start a game in the Liverpool midfield after easing him in during his first few months at the club. Lucas scored his first goal for Liverpool on 27 January 2008 when he curled a 25-yard shot into the top corner during an FA Cup match against Havant & Waterlooville, becoming the first-ever Brazilian to score for Liverpool.

Lucas returned with a bronze medal and Benítez had high hopes for the Brazilian’s future, stating, “This season he will improve because he is a very, very good professional and has experience of the Olympic Games.” Lucas noted that Liverpool’s squad was much improved from the previous season and relished the opportunity to compete for trophies, despite the increased difficulty of getting a first-team place. However, after a number of disappointing performances, both critics and fans voiced concerns about Lucas’ quality and his confidence was further knocked when Liverpool fans booed him after a lacklustre draw against Fulham. The criticism irked Benítez and he responded with a passionate defence of the player, saying that “people just don’t know how good Lucas is.” Benítez also underlined Lucas’ credentials, stating that he had been captain for both Grêmio and his national youth team, and that competing for place against Javier Mascherano, Steven Gerrard and Xabi Alonso was inherently difficult. Lucas’ performances in December 2008 for Liverpool drew him much praise from pundits, the highlight being his performance in the 5–1 thrashing of Newcastle United, where he provided an assist for Gerrard. Lucas was sent off in a cup tie against Mersey rivals Everton, which Liverpool lost. This compounded his growing unpopularity amongst Liverpool’s supporters, after he gave away a late penalty in Liverpool’s previous match, a 1–1 draw with Wigan Athletic.

On 19 August, Lucas was shown a red card in the 2008 Olympics semi-final match between Brazil and Argentina, after a challenge on then Liverpool teammate Javier Mascherano, as Argentina ran out 3–0 winners. In August 2009, Lucas was recalled to the senior Brazil squad in place of Flamengo’s Kléberson, who was absent through injury. After missing out on the Brazil world cup squad in South Africa, Lucas played the full 90 minutes in a friendly against the United States on 10 August 2010.

On 3 May 2009, Lucas scored his first Premier League goal, a header from a free-kick for Liverpool against Newcastle United in a 3–0 win.

On 8 April 2010, Lucas scored his second European goal for Liverpool, scoring in a 4–1 (5–3 aggregate) quarter-final win over Benfica in the UEFA Europa League quarter-finals.

In pre-season games before the 2010–11 season, Lucas was made captain of a youthful Liverpool side against Grasshopper. On 16 September 2010, Lucas scored his sixth goal for Liverpool shortly after replacing Ryan Babel in the club’s first Europa League group stage match against Steaua București. The goal was Liverpool’s third in a 4–1 victory and was scored from 22 yards. On 13 November, Lucas was sent off for the second time in his Liverpool career after being shown a second yellow card in injury time in Liverpool’s 2–0 defeat to Stoke City. On 6 December, Lucas was voted the fan’s pick for Man of the Match on the official Liverpool website. Lucas assisted a Ryan Babel goal in a 3–0 win over Aston Villa.

Lucas was awarded Liverpool Player of the Year Award in May 2011. On 30 March, Lucas signed a new long term contract at Liverpool.

After an excellent run of form for Liverpool, his season was unfortunately cut short on 1 December 2011, when it was confirmed he was out for the remainder of the season after he suffered an anterior cruciate ligament injury after he collided with Juan Mata in the 2–0 win over Chelsea in the quarter-final of the League Cup.

On 17 July 2011, Lucas was shown a straight red card in the 2011 Copa América play-off quarter final against Paraguay, after an extra time altercation with Antolín Alcaraz. Brazil went on to lose the match on penalties after the match had finished all square after 90 minutes.

On 10 April 2013, Lucas signed a new long term deal with the club. He was a consistent starter in the opening few months of the 2013–14 season as Liverpool put up an unexpected title challenge, though his season was again cut short by injury. His good form saw him make a return to the Brazilian national team’s squad.

Despite rumours of him leaving Anfield, Lucas was restored to the starting lineup. Following the sacking of manager Brendan Rodgers, Lucas under new manager Jürgen Klopp was praised for his excellent form in the club’s 11-game unbeaten run. Lucas made his 300th appearance for Liverpool on 26 January 2016 against Stoke City in the Football League Cup semi-final at Anfield. Lucas captained the side in the Premier League match against Crystal Palace on 8 November, a 2–1 defeat for Liverpool.

On 28 February 2016, Lucas started for Liverpool in central defence in the 2016 Football League Cup Final. He was one of three Liverpool players who failed to score his kick as the team lost 3–1 in a penalty shootout to Manchester City.

On 18 January 2017, Lucas scored his first goal for the club since 16 September 2010, a first-half header in the FA Cup 3rd round replay against Plymouth Argyle. The end of the season marked the completion of Lucas’s tenth year as a Liverpool player. In celebration, Lucas had a dinner party thrown in his honour and received a Special Recognition Award presented to him by club legend Kenny Dalglish at Liverpool’s postseason award ceremony.

On 18 July 2017, Lucas completed a move to Serie A side Lazio for £5 million, ending his 10-year stay at Liverpool.

Lucas made his official debut for the Rome club in a 3–2 win over league champions Juventus in the Supercoppa Italiana, on 13 August. His first goal for the club was in a 2–3 defeat to Zulte Waregem in the final group game of the UEFA Europa League. On 28 February 2018, Lucas missed a penalty during the penalty shootout in Lazio’s match against Milan in the semi-finals of the Coppa Italia; which Lazio eventually lost 4–5.