Liverpool did not provide details about the 26-year-old Firmino's new contract.
"The club have taken me in an incredible way and I've grown a lot here with my work with the support of the whole team. I am very happy here," Firmino told Liverpool's website.
"Everything fits in the best possible way. My team mates are fantastic and I am very grateful to be able to play with them at this club."
Liverpool are third in the Premier League and hopeful of reaching the Champions League final. They beat Italian Serie A side AS Roma 5-2 in the first leg of their semi-final last week.
"I love to play for Liverpool. The fans are excellent and fantastic in how they support us all the way. They support us throughout the games and the work they do during the match is beautiful," Firmino added.
(Reporting by Shrivathsa Sridhar in Bengaluru, editing by Ed Osmond)
