If the figure reported by Marca - worth £13.7m - is accurate, that means the Argentine whizkid will be paid €36.4m (£31.1m) a year before tax by the Catalan giants - or to put it another way £600,000-a-week.
It was announced in December that a deal had been reached to keep him at the Camp Nou - and that has now been signed.
A club statement read: "Leo Messi extended his contract with FC Barcelona through June 30 of 2018.
"The signing ceremony was attended by the player, president Sandro Rosell, vice-president Josep Maria Bartomeu and the director of football Andoni Zubizarreta.
"Messi added two additional years to his existing contract, which was set to expire in June of 2016. The player, who joined the club when he was 13 years old and made his first-team debut three years later, will be 31 when his contract expires."
Team-mate Jordi Alba was overjoyed at the news and said Messi could be regarded as the best player ever in a few years.
"I can’t imagine what Messi will be like in 2018, but it’s great news for Barça fans that he’s staying," he said.
"He is the best player in the world and as long as nothing happens, he’ll be the best ever. We’ll try to make him feel as comfortable here as we can."
Messi scored an incredible 92 goals in 2012 and is already regarded as a great of the game at the age of only 25.
He already has 34 goals in La Liga this season, netting in each of his last 12 league games, and has set a number of club scoring records.
Winning a fourth World Player of the Year award in January, he has been top scorer in the Champions League for four years in a row and has won that trophy three times alongside five domestic titles and two Copa del Reys.
Barca were held by Valencia last weekend, but hold a nine-point lead over Atletico Madrid at the top of La Liga while hated rivals Real Madrid in third are 16 points off their pace.
The Blaugrana host Getafe on Sunday.