Messi extended his stay with the Catalan club until 2018 last year, but had long been anticipated to agree an improved deal to make him the highest-paid player in world football.
An agreement was reached on Friday, despite the Argentinian having been involved in a war of words with Javier Faus in December after the club's vice-president said he saw no reason why Barca should improve Messi's contract "every six months."
Messi hit back by branding Faus as a businessman "who knows nothing about football", and has now put pen to paper having reached the 40-goal mark for the fifth straight season.
A club statement on Monday read: "FC Barcelona would like to announce that Leo Messi and the club signed a revised contract this afternoon.
"The signing took place in the presence of Leo Messi, his father Jorge Messi and the club president Josep Maria Bartomeu, as well as the sporting vice-president Jordi Mestre and the club CEO, Antoni Rossich.
"During the signing, which was made in the Presidential Box at the Camp Nou, Leo Messi repeatedly expressed his excitement about the new deal."
Despite Messi's continued excellence on the pitch, he was unable to inspire Barca to a last-day win over Atletico Madrid, which would have seen the Catalans win the Liga title.
A 1-1 draw secured the trophy for Atletico and also signalled the end of Gerardo Martino's Barca reign - the coach announcing his departure, by mutual consent with the club, immediately afterwards.
