Terms were not disclosed, but sources with knowledge of the deal say it's for five years and worth in the neighborhood of $5 million a year -- the richest shoe deal for an NFL player and about two times more than any previous deal Nike had with a football player.
Beckham's previous shoe deal with Nike was worth less than $1 million per year.
The deal will make Beckham a larger brand spokesman for Nike, including campaigns outside of football.
The deal grew so big because Adidas wanted to sign Beckham from Nike, sources said. Nike had the right to match the offer, which it did.
A Nike spokesman said the company wasn't commenting on the deal. The story was first reported by sneaker site NiceKicks.com.
"It was a long process," Beckham's agent, Zeke Sandhu, told ESPN. "This proved he's an icon."
Beckham's value comes from not only his flash on the field during games but also his ability to stay relevant off it. He has more than 8.3 million Instagram followers, 2.3 million Twitter followers and 1.3 million Facebook followers.
Beckham drew even more attention to himself and Nike with the shoes he wore before every game last year, customized by sneaker designer Troy Cole. One week, Beckham had Burberry Nikes; another week, it was a "Back to the Future" tribute. Every design seemingly spread like wildfire on social media before games.
The deal was done by Sandhu and Beckham Jr.'s mother, Heather Van Norman, who is his business manager.
On the field, Beckham is in the final year of his original four-year rookie deal with the Giants. He's set to make $1,839,027 in 2017 -- meaning Nike will play him far more than the team.
The Giants recently exercised a fifth-year option for 2018, which will likely pay Beckham more than $8 million. He can become a free agent in 2019 if the Giants don't use the franchise tag.
Information from ESPN.com's Jordan Raanan was used in this report.