On 26 July 2007, Lucas 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.
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.
The start of the 2008–09 season signified an important turning point for his career. Many commentators expected him to step up to the next level after completing his first season with the Reds. The Brazilian got off to a good start with a well taken opening goal in a 2–1 friendly win over Swiss side Lucerne in July. He impressed in pre-season games but missed the start of Premier League season due to his selection for the Brazilian Olympic Team in the Beijing Olympics.
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.[14] 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 14 March, Lucas played a key role[citation needed] in Liverpool's 4–1 victory over Manchester United at Old Trafford, starting in place of the injured Xabi Alonso. On 14 April, Lucas played against Chelsea in the Champions League, in place of Steven Gerrard. He scored a goal with his long-range effort in the 81st minute deflected off Michael Essien and past goalkeeper Petr Čech to make the score 3–3. Dirk Kuyt's header a minute later briefly gave Liverpool the lead, but Frank Lampard's 89th-minute strike leveled the score to 4–4, with Chelsea winning 7–5 on aggregate to go through to the semi-finals of the tournament.
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.
After an excellent run of form for Liverpool, his season was unfortunately cut short on 1 December, 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.
10 April 2013, Lucas signed a new long term deal with the club. Lucas was a consistent starter in the Liverpool 2013–14 side that put up an unexpected title challenge, though his season was again cut short by injury.[35] His good form saw him make a return to the Brazilian national team's squad.[36]
In the initial run of games within the 2014–15 Premier League and other cup competitions, Lucas was rotated in and out from the squad, leading to speculation surrounding a move away from Anfield. He made his comeback, however, as a starter against Ludogorets in the Champions League with a good display. His fine form continued and he started games against Stoke City, Leicester City and Sunderland. Lucas' good run continued as Liverpool then played against Manchester United, Arsenal, Burnley, Swansea City, Leicester and Sunderland out of which Liverpool only lost to United and then achieved five games without defeat in a row with Lucas as an integral member. Lucas was on the substitute bench on 22 March in a 2–1 defeat against Manchester United after coming back from a six-week injury layoff.
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.[47] 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 honor 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
