Martina Navratilova won a mixed-doubles championship at the US Open at the age of 49, and then retired for the second time. I don’t think she played another match.
Bruce(now Caitlyn) Jenner,after winning the Olympic decathlon in 1976, left his (her?) vaulting poles on the field as he (she?) had no intention of ever competing again.
Ed Charles of the 1969 Mets retired after the final game of that year’s world series
If coaches can be included in this list…
John Wooden won the last of his 10 NCAA championships in the final game he coached, in 1975.
Elway was already mentioned.
Ray Lewis retired after winning his 2nd Super Bowl. 49ers star lineman Randy Cross retired after beating the Bengals in XXIII.
Bill Walsh also retired after winning Super Bowl XXIII
At the time Olympic athletes pretty much had to do that so they could earn some money. For that reason you could probably list quite a few from that era. Jenner was probably the most high profile of the bunch.
After beating the Patriots in the Super Bowl and spoiling their perfect season, Michael Strahan retired.
Whitworth did something maybe no one else did. He sat his children down on the field as the celebration was going on and told them he was retiring to spend more time with them:
I assume we’re not including college athletes, as any number of college seniors have won championships across an array of team and individual sports and never again competed.
Four years before Jenner, swimmer Mark Spitz, who won seven golds at Munich, was another who retired from the sport immediately after the Olympics – he went into acting and sports announcing for a time, then various business ventures.
But, Spitz then came out of retirement in 1992, at age 41, when he was offered $1 million by filmmaker Bud Greenspan if he would attempt to again qualify for the U.S. Olympic swimming team (and have his efforts filmed). He turned out to be substantially slower than the qualifying times, and as far as I can tell, retired again, for good.
I thought Tom Watson deserved a mention here. He made it to a sudden death playoff in his last master’s tournament.
You may be thinking of the 2009 Open Championship (a.k.a. the British Open), which Watson lost in a playoff, at age 59.
But, Watson then played in the British Open six additional times after that year, as well as continuing to play in the other three majors (Masters, U.S. Open, PGA Championship), though he typically didn’t make the cut at that point in his career. He also kept playing on the Senior Tour, and won the Senior PGA Championship in 2011. Watson didn’t actually retire from competitive golf until 2019.
Tyler George was a member of the U.S. men’s curling team that won gold at the 2018 Winter Olympics. He retired from top-level competition after that. The rest of the team stayed together and finished fourth in 2022.
Andre “Son of God” Ward won the vacant Ring light-heavyweight championship with a TKO over Sergei Kovalev in his final boxing match. He held all the important light-heavyweight titles already. He then retired citing his physical condition and lack of desire as reasons. This put him in the exclusive club of boxing champions retiring undefeated along with Rocky Marciano, Joe Calzaghe, and Floyd Mayweather, and a few lesser known fighters.
That’s who I was going to mention. He’s certainly the most memorable: He scored the cup-winning goal in overtime against the Montreal Canadiens, then vanished on a fishing trip when his plane went missing. HIs body wasn’t discovered for 11 years. And the capper to the story is that the Leafs never won a cup the whole time his body was missing, but won again the year they found him.
As the Hip sang:
Bill Barilko disappeared that summer
He was on a fishing trip
The last goal he ever scored
Won the Leafs the cup
They didn’t win another till nineteen sixty two
The year he was discovered
You stole that from a hockey card you kept tucked up under…
Honourable mention to Jochen Rindt, the first (and hopefully last) posthumous winner of the F1 world championship. He was killed in a race prior to the end of the 1970 season, but no-one else was able to overhaul his accumulated points total in the remaining races, so he was champion. Doesn’t fit the OP of course - almost the opposite.
If coaches are allowed, Sir Alex Ferguson won the English Premier League title in his last season as manager of Manchester United. His very last game was a 5-5 draw - a very unusual result in modern professional football. But they had already secured the title by then.
A number of boxers have retired undefeated, but not all of these fit the criteria of the OP - for example, Floyd Mayweather unretired for a non-title bout against Conor McGregor, so his final fight was not winning a championship. Rocky Marciano is probably the most famous of those who I think do qualify.
November 2000. A 31 year old Akebono, who’d been battling injuries, the merciless Futagoyama juggernaut, and extremely rude reporters for years, steamrolled through the tournament en route to a dominating 14-1 yusho. Other than blazing phenom Kotomitsugi (13-2), no one else, including Musashimaru and Takanohana, was better than 11-4.
Akebono missed the entire January 2001 basho and announced his retirement soon after.
It’s not hard to find cases like this in team sports. Just look at the roster of a championship team and see if there are any players who never played again. There are lots of non-superstar players like this.
For instance, Dick Green, second baseman for the Oakland A’s, played in the last game of the 1974 World Series, then retired. He was an important member of the team, but even most serious fans today have never heard of him.
Marciano didn’t win a title in his last fight. It was just another defense for him. Granted, at that time there was not the ‘alphabet soup’ of boxing titles that boxers can vie for at the present time.