LeBron James has signed an exclusive partnership with Polymarket, while five-time Grand Slam champion Maria Sharapova has fronted a separate campaign for the prediction market’s tennis product. The two deals became public within days of each other in early September, as Polymarket leans harder on athletes alongside the league, data, and streaming partnerships it has been stacking up all year.
James announced his deal on Sept. 5 with a 14-second video showing him walking into a fictional Polymarket headquarters and taking an elevator to a floor marked “sports.” A representative said the post previews a larger campaign starting this week, beginning with American football. Financial terms haven’t been disclosed, and neither side has said whether equity is part of it. James’ previous endorsement deal with DraftKings expired earlier this summer.
NBA rules restrict active players from holding certain financial interests in businesses offering NBA-related wagering products, which makes the structure of this agreement worth watching. James is the first active NBA player to sign individually with Polymarket, though Kalshi already has Milwaukee Bucks star Giannis Antetokounmpo as an investor. Antetokounmpo became a shareholder in February through his company Ante Inc. and is prohibited from trading NBA-related markets.
Sharapova promoted Polymarket on Sept. 3 in a social media video about trading during live tennis matches. Her campaign follows Polymarket becoming the ATP Tour’s official prediction market provider in August, which gave the platform exclusive prediction-market streaming rights for ATP Tour and ATP Challenger Tour matches. Polymarket hasn’t disclosed the financial terms with Sharapova or announced any investment by the retired player.
The ATP agreement lets registered US users watch live matches next to the related markets, with official real-time data supplied through Sportradar. It covers around 20,000 ATP and Challenger matches a year, giving Polymarket a direct connection between sports streaming and event contracts instead of only branding around competitions.
US tennis has split between the two biggest prediction exchanges. Kalshi signed a multi-year agreement with the USTA on Aug. 31 to become the US Open’s first official prediction market partner, while Polymarket holds the ATP Tour and Challenger Tour. Sportradar separately expanded its Polymarket agreement on Aug. 27 to include official data for the tennis Grand Slams and several other sports properties.
Polymarket has moved into mainstream sports partnerships quickly during 2026. Major League Baseball made it the league’s exclusive official prediction market exchange in March, and the expanded Sportradar agreement now provides data, streaming, and integrity services across more than 20 leagues and competitions, roughly 300,000 matches a year. That coverage includes the Bundesliga, Euroleague Basketball, the Chinese Basketball Association, Australia’s NBL, Grand Slam tennis, and UTR Pro events.
James had already shown how valuable a major athlete can be to these platforms before signing with one. Contracts tied to his 2026 free-agency decision generated more than $273 million in trading volume across prediction platforms before he joined the Philadelphia 76ers, with tens of millions traded through Polymarket alone. The new campaign gives Polymarket direct access to an athlete whose career decisions have already produced that much activity on the product.
The athlete deals are developing while prediction markets remain caught in a wider US regulatory dispute over sports event contracts. Polymarket’s US operation runs through a federally regulated exchange under Commodity Futures Trading Commission oversight, while several states argue that sports contracts should also fall under state gambling laws. New Jersey asked the US Supreme Court on Sept. 2 to examine that question in its case against Kalshi, which could produce a decision affecting the whole sector.
James and Sharapova give Polymarket two recognizable faces for the sports categories it has spent much of 2026 building out through rights and data agreements. He fronts a football campaign as the NFL season starts, and Sharapova’s promotion connects to the tennis product the ATP deal created. Polymarket is now pairing the infrastructure behind sports prediction markets with the same athlete-led marketing sportsbooks have always used.