Coutinho, who moved to Anfield from Inter in January 2013, was already under contract with Liverpool until 2018 but he has been rewarded with a renewed deal on the back of some impressive performances in recent weeks.
The 22-year-old laid on both goals during Saturday's 2-0 win over West Ham and
"Today I've committed my future to the club and for this I'm feeling very pleased," he said. "This club is great and the fans have always supported me, so I've been eager to sign this new deal since conversations started. Today is a very happy day.
"It means so much. This club has given me the opportunity to play and believed in me even though I hadn't been playing regularly at my previous club.
"I've had a great reception since my first day here. As I always say, Liverpool is a big family and I'm a happy person here."
Coutinho has scored twice in 31 appearances across all competitions this season.
