He had just signed a record $325 million, 13-year contract and conceded he wasn't certain he should have agreed to the deal.
"There was no 100 percent sure answer," Stanton said. "But the decision is made. Once you make your decision, you go all-in with it."
The slugger hit the jackpot, landing the most lucrative contract for an American athlete and the longest in baseball history. Stanton accepted the deal after cost-conscious owner Jeffrey Loria pledged to put together a contending team that will finally transform Miami into a baseball town.
Stanton and South Florida have heard such talk before.
"You can't keep saying, 'We're going to win this year. We're going to do it this year,'" Stanton said. "I'm sick of hearing that. Everyone is sick of hearing that. It's doing something about it."
At a news conference, Loria said signing Stanton is part of a long-range plan that began with the Marlins' most recent payroll purge two years ago.
"Our goal was to start fresh," Loria said. "It wasn't popular, but we had to do it. We wanted to create a long-term system around young players who would build their entire career with us."
General manager Dan Jennings said the team plans to pursue multiyear contracts this offseason with several other young players, including right hander Jose Fernandez, center fielder Marcell Ozuna, left fielder Christian Yelich and shortstop Adeiny Hechavarria.
Such deals will be possible for the historically low-payroll franchise only because of the way Stanton's contract is structured. He readily agreed to a heavily backloaded agreement, and will make just $6.5 million in 2015, the same as this year. His salary doesn't peak until 2023, when he'll make $32 million.
"It's an exciting day for Miami, my fans, our fans,'' Stanton said. "This is not a lottery ticket. This is the start of work and a new job. It's a huge responsibility, and one I'm willing to take.''
The agreement wouldn't have happened without such structuring, team president David Samson said. He said the Marlins anticipate better attendance and a more lucrative TV package will make Stanton's contract affordable.
Loria wants to be around for the franchise turnaround. His popularity with fans has plummeted in recent years, but he has no plans to sell the team, Samson said.
"He's in it with Miami for the long run, because he loves it," Samson said.
"This is not a lottery ticket. This is the start of work and a new job. It's a huge responsibility, and one I'm willing to take."Giancarlo Stanton
While Kevin Brown became the first player to break the $100 million barrier in 1998 and Alex Rodriguez became the first to top $200 million just two years later, it took 14 more years to produce baseball's first $300 million man.
Stanton took the podium for his news conference wearing a tailored blue suit and a grin, showing no signs of the beaning that ended his season Sept. 11. He hasn't hit a ball since but said he'll return to the batting cage beginning in mid-December in his native California.
"I'll probably take a moment before I get into that box, but it'll be good," he said. "I'm excited for it."
The Marlins said they're not concerned the injuries will have lingering effects.
Stanton, who turned 25 on Nov. 8, wasn't due to become eligible for free agency until after the 2016 season. When negotiations on his mega-deal began, Stanton said he was more concerned about the front office's plans for improving the roster than about his financial terms.
Despite 154 home runs from Stanton, the Marlins have finished with a losing record in each of his five seasons, including three last-place finishes.
"They had the contract there, and I put it aside and said, 'Listen, what are we going to do to make this better?'" Stanton said. "I'm financially good for the rest of my life. Great. But I'm not coming here to get my butt kicked for 10 hours every day and then going home to a lavish lifestyle. That's not fun for me."
He said he didn't seek advice from players on other teams about whether to accept the Marlins' offer.
"Everyone sees the dollar sign and they're like, 'What are you waiting for?' No one could relate to how I felt over the years. So I had to do this on my own."
The final hurdle in negotiations was an opt-out clause, which Stanton described as "my fail-safe." He can part with the Marlins after making $107 million over the first six years of the deal. It also includes a no-trade clause.
In the end, Stanton called the decision to say yes the toughest of his life.
"This is 13 years," he said. "I didn't even go to school for 13 years."
He signed the agreement at the start of the news conference, Loria at his side.
"I'm glad to be here for my foreseeable future," Stanton said.
The occasion attracted nearly 100 members of the media, a sign interest in the Marlins already is on the rise.
The team trumpeted its new-found optimism on Twitter: