The Argentina superstar could have walked away from the LaLiga giants on June 1, a date he can unilaterally terminate his deal and leave as a free agent.
However, Messi chose not to trigger the clause and will now stay at the Nou Camp for one more year.
In theory, the 32-year-old will be able to speak to foreign clubs from January under the FIFA rules, but Barca will be hoping to agree fresh terms with the player.
Messi has been linked with a move away this year after he made comments about some of the senior figures at the club.
He also had a public face-off with sporting director, Eric Abidal.