"FC Barcelona and Lionel Messi signed on Saturday morning a new contract that will keep the Argentine superstar at the Club through the 2020/21 season," said a statement from Barca, posting a picture of Messi signing the deal alongside president Josep Maria Bartomeu.
"The buyout clause was set at 700 million euros (626.25 million pounds)."
Messi, 30, agreed the new contract with Barcelona in July but the club did not release the usual photo of the player putting pen to paper, fuelling speculation he could depart in June 2018, when his previous deal ran out, for free.
Messi is Barca's all-time top scorer with 523 goals in all competitions and has won eight Liga, five King's Cup and four Champions League titles since making his debut for the Catalan club in 2004, having joined their youth academy in 2000 aged 13.
He leads the scoring charts in La Liga with 12 goals and on Friday picked up the 2017 European Sports Media Golden Shoe for being the top scorer in a domestic league last season with 37 goals.
Barca can extend their lead at the top of La Liga to seven points if they beat second-placed Valencia on Sunday.
"We should have signed this a long time ago and now we have and I'm happy to continue with the club, which is my home," Messi told Barca's official television channel.
"My dream was to finish my career at Barça and we are moving down that path. Our objective is to continue achieving great things, fill the trophy cabinet and keep making history.
"We've been lucky enough to have won a great many things and I hope there will be more in the future."
Barca president Bartomeu hinted that Messi's buy-out clause had been cranked up from 300 million euros in the agreement in June up to 700 million euros after the club lost Neymar to Paris St Germain in August after the French giants paid the Brazilian international's clause of 222 million euros.
"It's a new contract that we have signed today, because although the one we signed in June was up to par with his greatness as a player, the new one is more in line with the current situation in the ever-changing world of football," Bartomeu said.
"It's a great contract for the best player in football history. It fills me with pride to see him with us renewing his love for the club."
($1 = 0.8382 euros)
(Reporting by Richard Martin; Editing by Rex Gowar and Ian Chadband)
