Barcelona Football club president: Josep Maria Bartomeu described him as "the best player in football history", and said the new contract, with a significantly higher buyout clause, was "more in line with the current situation in the ever-changing world of football".
He Said that the buyout clause had to be modified, and it has gone from 300m euros to 700m euros.
"It fills me with pride to see him with us renewing his love for the club."
Messi was presented with his fourth European Golden Shoe on Friday - the award given to the highest scorer in European club football - after finding the net 37 times in La Liga last season.
Barcelona forward Lionel Messi said he had moved closer to his "dream" of "finishing my career at home" after signing a new contract, with the buyout clause raised to 700m euros (£626m).
Messi's new deal will expire after the 2020-21 campaign. The 30-year-old had one year remaining on his old contract.
The Argentine international, a five time Ballon d'Or winner, has scored 523 goals in 602 appearances for Barca.
"The objective is to continue achieving things and making history," he said.
Since joining at the age of 13, Messi has helped Barca win eight Spanish league titles and the Champions League four times.
"We've been lucky enough to have won a great many things and I hope there will be more in the future," he added.
"I'm happy to continue with the club, which is my home. My dream was to finish my career at Barca and we are moving down that path."
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