Giannis Antetokounmpo redoubled his commitment to the only N.B.A. franchise he has known by signing a five-year contract extension worth an estimated $228 million from the Milwaukee Bucks.

Six days before a Dec. 21 deadline to either sign the so-called supermax extension or become an unrestricted free agent after this season, Antetokounmpo on Tuesday released a statement via his social media channels proclaiming himself “blessed to be able to be a part of the Milwaukee Bucks for the next 5 years.”

“This is my home, this is my city,” Antetokounmpo wrote.

In a team statement later Tuesday confirming the deal, Antetokounmpo said: “You took a chance on us eight years ago and now putting my signature on a contract like this is unreal — but it’s all because of hard work. This is my home and I’m going to continue working hard and do my best to make the Bucks, our fans and the city proud. Let’s have fun, win and make these years count.”

The Bucks selected Antetokounmpo, who was born and raised in Greece by Nigerian parents, with the 15th overall pick in the 2013 draft, despite Antetokounmpo’s limited professional experience in the Greek second division. Antetokounmpo has blossomed beyond all expectations to win back-to-back Most Valuable Player Awards and, by committing his long-term future to the Bucks, has delivered the team its most significant victory since Kareem Abdul-Jabbar and Oscar Robertson led Milwaukee to its lone N.B.A. championship in 1970-1971.

“This is one of the great days in Bucks history,” Peter Feigin, the Bucks’ team president, said during a virtual meeting organized by the Milwaukee Press Club shortly after Antetokounmpo revealed the news.

Antetokounmpo, who turned 26 on Dec. 6, is under contract for one more season on his current deal and, because he signed an extension, cannot be traded by the Bucks before next season. The extension is the largest contract in N.B.A. history, surpassing the five-year, $207 million contract Russell Westbrook signed to stay with the Oklahoma City Thunder in September 2017. Antetokounmpo’s new deal includes a player option after the 2024-25 season that would allow him to enter free agency one year early.

After winning M.V.P. honors for the first time in 2018-19, Antetokounmpo averaged 29.5 points, 13.6 rebounds and 5.6 assists per game last season to repeat as M.V.P. He was also named Defensive Player of the Year last season, joining Michael Jordan (1987-88) and Hakeem Olajuwon (1993-94) as the only players to win the M.V.P. and defensive player awards in the same season.

The Bucks posted the league’s best regular-season record in each of the past two seasons but have had back-to-back playoff disappointments, which led to considerable apprehension in Milwaukee that Antetokounmpo might pass on the extension and choose a new team next season. After a meek second-round playoff series loss to the Miami Heat this summer, Bucks officials promised Antetokounmpo that they would upgrade the roster — and they duly agreed to a trade in November to acquire the highly rated guard Jrue Holiday from the New Orleans Pelicans.

But a planned sign-and-trade deal with the Sacramento Kings to acquire the sharpshooting restricted free agent Bogdan Bogdanovic in addition to Holiday collapsed and, as The New York Times first reported, prompted the league office to open an investigation. The N.B.A. is exploring possible violations of its anti-tampering rules, since it appeared that the Bucks and Kings had already reached an agreement on a sign-and-trade transaction more than three days before free-agent discussions of any kind were allowed to start. Bogdanovic eventually joined the Atlanta Hawks after he signed a four-year, $72 million offer sheet with the Hawks that Sacramento elected not to match.

Tuesday’s announcement ended a nervy period for the Bucks since the Holiday acquisition and the Bogdanovic drama, sparing the small-market franchise from the specter of constant questions about Antetokounmpo’s future as the Bucks try to make it back to the N.B.A. finals for the first time since 1973-74. After that season, Abdul-Jabbar quietly asked Milwaukee to trade him, saying he preferred to live in New York or Los Angeles. The request ultimately led the Bucks to trade Abdul-Jabbar to the Los Angeles Lakers in June 1975.

In a 2017 interview with The Times, Antetokounmpo described himself as “a low-profile guy” who had no interest in “all these flashy cities like L.A. or Miami.”

“I don’t know if I could be the same player if I played in those cities,” Antetokounmpo said then.

Teams such as Miami, Toronto and Dallas had been managing their payrolls in hopes of making a free-agent run at Antetokounmpo in 2021, but to the Bucks’ great relief, teams in flashier markets won’t get that chance.