The former San Francisco 49er superstar unveiled the ad on Twitter.
Nike recently announced that Kaepernick will be a major part of the 30th anniversary of its "Just Do It" campaign, with the ad featuring the former quarterback reading, "Believe in something, even if it means sacrificing everything," alluding to his kneeling protest over social injustice that has seemingly cost him his job.
Nike has been hit with outpourings of both support and criticism, with many calling for a boycott and social media videos showing people destroying Nike apparel.
President Donald Trump weighed in, saying Nike is getting "killed." Trump said on Twitter on Wednesday, "Just like the NFL, whose ratings have gone WAY DOWN, Nike is getting absolutely killed with anger and boycotts. I wonder if they had any idea that it would be this way?"
Just like the NFL, whose ratings have gone WAY DOWN, Nike is getting absolutely killed with anger and boycotts. I wonder if they had any idea that it would be this way? As far as the NFL is concerned, I just find it hard to watch, and always will, until they stand for the FLAG!— Donald J. Trump (@realDonaldTrump) September 5, 2018
Trump has repeatedly slammed NFL players for kneeling in protest during the national anthem and says he'll find it difficult to watch the NFL "until they stand for the FLAG!"
Others, including Lebron James, say they're proud of Nike. Clutching his young daughter in his arms, the new member of the Los Angeles Lakers made the remarks as he received an award Tuesday for both his style and his philanthropy from Harlem's Fashion Row. The fashion collective partnered with Nike for the New York event, both a fashion show and an awards ceremony that focused on diversity in the fashion world. The evening culminated in the reveal of the latest LeBron James Nike basketball shoe: A women's sneaker designed by three female African-American designers and inspired by strong African-American women.
Closing his remarks, he said he stood "for anybody who believes in change." He added: "I stand with Nike, all day, every day."
VIDEO: Bay Area Army veteran who encouraged Kaepernick to take a knee addresses new Nike ad
Kaepernick's attorney Mark Geragos announced the endorsement deal on Twitter, calling Kaepernick an "All American Icon."
Kaepernick already had a deal with Nike that was set to expire, but it was renegotiated into a multiyear deal to make him one of the faces of Nike's 30th anniversary "Just Do It" campaign, according to a person familiar with the contract. The person spoke to The Associated Press on condition of anonymity because Nike hasn't officially announced the contract.
The person said Nike will feature Kaepernick on several platforms, including billboards, television commercials and online ads. Nike also will create an apparel line for Kaepernick and contribute to his Know Your Rights charity, the person said. The deal puts Kaepernick in the top bracket of NFL players with Nike.
Nike also provides all NFL teams with game-day uniforms and sideline apparel, a partnership that was extended in March to run through 2028.
TIMELINE: Looking back at Colin Kaepernick's transformation from football star to social justice advocate
Last week, Kaepernick scored a legal victory in his grievance against the NFL and its 32 teams when an arbitrator allowed his case to continue to trial. The quarterback claims that owners conspired to keep him out of the league because of his protests of social injustice.
Kaepernick contends the owners violated their collective bargaining agreement with players by conspiring to keep him off teams. His case hinges on whether owners worked together rather than decided individually to not sign Kaepernick.
A similar grievance is still pending by former 49ers teammate Eric Reid, a Pro Bowl safety who joined in the protests.
On Friday night, Kaepernick and Reid, also now out of the league, were each given huge ovations when they were introduced and shown on the big screen during a match between Serena and Venus Williams at the U.S. Open.
VIDEO: Kaepernick billboard hangs high above SF's Nike store
Meanwhile, the league and players union still haven't resolved whether players will be punished this season if they choose to kneel or demonstrate during the national anthem. Owners approved a policy requiring players to stand if they are on the sideline during "The Star-Spangled Banner," allowing them to stay off the field if they wish.
But the league and union put that on hold after the Miami Dolphins faced backlash for classifying the protests as conduct potentially detrimental to the team - putting players at risk of fines or suspensions.
Get the latest on former 49er quarterback Colin Kaepernick here.
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The Associated Press contributed to this report.