The decision, announced in a video interview published by Goal.com, comes after days of intense speculation sparked by Messi's attempt to unilaterally rescind his contract on Aug. 25. Messi and his legal team argued on Friday that he had exercised a clause that enabled him to leave without financial penalty at the end of each season.
"I would never take the club I have played my entire life for to court, and that is why I am staying in Barcelona. It was a tough decision. I always said I wanted to end my career here and I do," Messi said.
Barcelona has said the exit clause expired in June and that Messi's deal -- which runs until 2021 -- is still valid. They claimed that if Messi wanted to leave, he or his next club would have to pay his €700 million release clause or face legal action.
La Liga backed up Barca's position, saying they would not process Messi's transfer unless his buyout clause was paid. That stance was criticised by Messi's father, Jorge, in a letter sent to La Liga on Friday, insisting that the €700 million fee was no longer applicable.
Jorge -- who is also his son's agent -- had arrived in Barcelona on Wednesday for a face-to-face talk with team president Josep Maria Bartomeu. Sources told ESPN that the meeting was positive and constructive, and Barca were not ruling out Messi staying for another season.
"For some time now we have not had a plan or anything [at the club], we have been making quick fixes and improvising," Messi said, adding that the burofax he sent to the club announcing he wanted to leave "was only to make it official that I wanted to go, because the president was not paying attention to what I was saying."
The club believed the player's motivation in all this was a desire for new challenges, which he could pursue, if he wished to, from 2021. Messi, in his statement, confirmed his frustrations at the lack of innovation by the club.
"I'm going to stay at the club because the president told me the only way to leave was to pay the €700m clause, which is impossible, and that the alternative was going to court. I would never take Barca to court ever, because it's the club I love," Messi said.
He added: "All year I've been telling the president I wanted to leave, that the time had come to look for new challenges in my career. .... Sending the burofax was making it official that I wanted to leave and that I'd go for free, I wasn't going to use the optional year and I wanted to go. It wasn't meant to cause trouble, or to go against the club, it was a way of making it official because my decision was taken."
Messi said he felt his pleas had been ignored by club management.
"What they say is that I didn't tell them before June 10, but we were in the middle of all the competitions and it wasn't the moment," Messi said. "As well, the president always said to me, 'When the season is over, you decide if you want to stay or go' -- he never said a date, and it was simply to make it official that I wasn't carrying on. It wasn't to start a fight, because I didn't want to fight with the club."
He added that the frustration he expressed had built up over time and was not just due to the team's Champions League exit.
Messi will now rejoin his teammates to lead new Barca coach Ronald Koeman's revamped team this season as they try to improve on a trophyless 2019-20 that saw them finish behind Real Madrid in La Liga and be knocked out of the Champions League in a humiliating 8-2 quarterfinal defeat to Bayern Munich.
"It doesn't come from the Bayern result, it comes from many things," Messi said. "I always said I wanted to end my career here, and I always said I wanted to stay here. I wanted a winning project and to win trophies with the club. ... The truth is that for a while there hasn't been a project or anything, they've been juggling things and plugging holes as things happen. I've always thought about the well-being of my family and the club."
Those plans have now been put on hold, though, after Messi changed his mind in the face of a prolonged, acrimonious standoff.
The 33-year-old had been refusing to attend training sessions with the team in the belief that doing so would undermine his legal case.
Barca's sole reaction following the announcement was to tweet an image of Messi, using one quote from his interview: "I will give it my all. My love for Barca will never change."