Antetokounmpo is following the model of Kansas City Chiefs quarterback Patrick Mahomes: small-market star investing in the local baseball franchise, which Mahomes did in joining the Kansas City Royals' ownership group.
"Man, this is unbelievable,'' Antetokounmpo, wearing a No. 34 baseball jersey, said at Friday's news conference. "This is a dream come true for a kid from Sepolia, Athens, Greece, born from immigrant parents. I could have never imagined I would be in this position.''
Brewers principal owner Mark Attanasio joked that he wondered whether president of baseball operations David Stearns might want to try out the 6-foot-11 forward at first base.
"We are honored to have Giannis join our team of Milwaukee Brewers investors," Attanasio said in a statement. "Giannis is a great athlete, a world champion, and a true local hero with international renown."
Antetokounmpo is the first new individual investor who has been added to the Brewers ownership group since Attanasio purchased controlling interest of the franchise in 2005.
The decision by the two-time NBA MVP to buy into the city's baseball team comes one month after he helped lead the Bucks to Milwaukee's first NBA title in 50 years.
Attanasio and Antetokounmpo said they finalized this agreement in May. Antetokounmpo said he and the team kept it quiet at the time because they didn't want to distract from the Bucks' playoff run and the early part of the Brewers' season.
"Milwaukee made me who I am today,'' said Antetokounmpo, who signed a five-year, $228 million supermax contract extension with the Bucks in December. "It made me a better person. This is basically my home. I've become a father here. I've become a leader here. I've become a champion here, and I want to be involved.
"I want to be involved in the community as much as possible. I know Milwaukee invested a lot in me, and I want to invest a lot of me back into the city of Milwaukee.''
Antetokounmpo said he started thinking about getting involved in ownership of a pro sports franchise last year while he was in the NBA playoff bubble at Walt Disney World. Antetokounmpo, who is from Greece, said his team first discussed the possibility of buying a European soccer club.
The Brewers appear to be a sound investment. The team holds a 7½-game lead in the NL Central entering play Saturday.
"Obviously growing up in Europe, there's not a lot of baseball over there,'' Antetokounmpo said. "I can tell you when I was introduced to baseball. I was 18. It was the first day I came to Milwaukee. I came to a game. But I know Christian Yelich. I know he's a great player.''
Antetokounmpo can talk to the Brewers players about the benefits that come from winning a title.
"It's hard to get it done," Antetokounmpo said. "It's hard to get there. But once you accomplish that, it's the best feeling ever. It's the best feeling ever. You always remember what it took to get there. And you create this bond with your teammates for the rest of your life. It's an addictive feeling."
Attanasio said about 20 Brewers players were watching from a Fiserv Forum suite when Antetokounmpo scored 50 points in Game 6 of the NBA Finals to clinch the Bucks' first championship since 1971.
"We're trying to have some of that good karma that Giannis and his teammates created to rub off on us," Attanasio said.
Antetokounmpo isn't the only notable Wisconsin athlete with an investment in another of the state's pro franchises. Green Bay Packers quarterback Aaron Rodgers has a minority ownership stake in the Bucks.
ESPN's Jeff Passan and The Associated Press contributed to this report.