The Brazilian has made 208 appearances for the Reds since joining from Gremio in July 2007.
Liverpool: Liverpool midfielder Lucas Leiva signed a new long-term contract on Wednesday, underlining his importance to the Premier League club after returning from a lengthy injury absence this season.
Lucas, who had a mixed start to his Anfield career, became a fans' favourite with a string of dynamic displays before he suffered a serious knee injury that ruled him out for six months last season.
His return to the starting lineup at the beginning of the new campaign was short-lived as he picked up a thigh injury that left him kicking his heels on the sidelines for another three months.
Since returning in December, the Brazilian has shown glimpses of his best form while his presence at the heart of Liverpool's midfield has coincided with a significant improvement in the team's results.
"It's another long-term contract that I have signed - but it was the same feeling as when I first came here," Lucas, who has 20 caps for Brazil, told the club website (www.liverpoolfc.com).
"I am really delighted to have the opportunity to play for this club. It's where I think I belong and where I wanted to stay, so I am very happy and looking forward to a few more years here.
"It was an easy decision because after the long period of my career I have had here, I would like to give the best of my time to this club. It was not a difficult decision to make and I am really looking forward to what will hopefully be a few more years with a lot of success."
Lucas struggled to sparkle at the start of his Liverpool career and was frequently dismissed as a mediocre battler with little real quality. He was reportedly close to strolling out of the Anfield exit during the 2010 close-season under former manager Roy Hodgson with a host of European also-rans touted as a possible destination.
As Liverpool began to rebuild under manager Kenny Dalglish, the 26-year-old, who was signed from Gremio in 2007, quickly became central to their improvement. His long-term injury absence coincided with a drop off in the team's form in the second half of last season and arguably contributed to Dalglish's sacking in May.
"He just goes from strength to strength," said managing director Ian Ayre. "We said throughout last summer and January, we wanted to keep our best, experienced players, and this is another great example of that."
"The manager has said several times that as well as having a great, young squad, it's important we have experience and it's important we have characters. People like Lucas fit that.
"He'll tell you he's still very young, but in footballing terms he's experienced and a big part of the team."