Stanton signed the deal at the start of the news conference Wednesday while sitting next to owner Jeffrey Loria. The attendance-challenged franchise drew nearly 100 members of the media for the occasion.
"Everyone wants to talk about the record-breaking deal and all that," Stanton said. "I want to have records on the field and do things on the field. That's what this is all about."
Said Marlins president David Samson: "Giancarlo, the first thing he said was, I want to win and I want to win in Miami."
The contract is the most lucrative ever for an American athlete and the longest in baseball history. It includes a no-trade clause, and Stanton can opt out after six years and $107 million.
The Marlins hadn't held a celebratory news conference on such a scale since their last spending spree, just before their ballpark opened in 2012. They went 69-93, leading to a payroll purge.
Earlier Wednesday, the Marlins tweeted out that things were just about done:
If Stanton opts out of the after the first six seasons, he'll be walking away from a staggering $218 million over the final seven seasons, sources familiar with the deal told ESPN.com Tuesday.
However, one source said Stanton was so motivated to give his team the financial flexibility to win now, he agreed to a heavily backloaded contract structure that will pay him just $30 million over the first three seasons.
According to a major league source who had seen the terms, Stanton's salaries over those first three seasons will be only $6.5 million in 2015, $9 million in 2016 and $14.5 million in 2017, far less than he could have earned through arbitration in 2015 and 2016 and then via free agency. He would earn $77 million over the next three seasons and could opt out of the contract after 2020, following his age 30 season.
Information from The Associated Press is included in this report.