A crowd gathered around the playing field responded with a standing ovation.
"I may come back and do this again because it isn't often that the Commissioner gets a standing ovation," Selig said, smiling.
It will be the city's third All-Star Game and the second for the Royals, who played host to the 44th game, in 1973.
Selig had promised in 2006 that Kansas City would get a Midsummer Classic between 2010-14 if a tax referendum to fund stadium renovations was passed. Jackson County taxpayers said yes, and the $275 million in improvements were completed last year.
On Wednesday, Selig delivered on his promise with what will be MLB's 83rd All-Star Game.
"It is estimated that revenues from the Midsummer Classic will amount to $70 million to Kansas City and its environs," Selig said.
He later estimated that local charities would benefit by $4 million or more.
Selig was accompanied by Royals owner David Glass and a bevy of dignitaries that included Missouri governor Jay Nixon, Jackson County executive Mike Sanders and Kansas City mayor Mark Funkhouser. Hall of Fame broadcaster Denny Matthews emceed the event, which ended before rain came to delay the start of the Royals-Astros game.
Serving as a backdrop to the ceremony were 30 young players from the local RBI program -- Reviving Baseball in Inner Cities -- each one wearing a jersey from one of the Major League clubs.
Also on hand were Dan Glass, the Royals' team president; Kevin Uhlich, Royals senior vice president for business operations, who spearheaded the renovations; Dayton Moore, the Royals' general manager, and Royals Hall of Famer John Mayberry, who had two hits in the 1973 All-Star Game, played at what was then called Royals Stadium.
Selig saluted David Glass.
"His leadership throughout the process and his successful efforts in renovating Kauffman Stadium were key factors in rewarding this game to Kansas City," Selig said. "The competition among our 30 clubs to play host to an All-Star Game has become incredibly intense in recent years."
Kansas City also was home to the first of two 1960 All-Star Games, hosted by the Athletics at old Municipal Stadium.
"You will discover that the 2012 event will be much bigger and much better," Selig said in a news conference later. "All-Star Summer will give fans the opportunity to experience various celebrations of our game over a five- or six-day period in which fans will be able to reach out and touch our great game."
Included will be the Futures Game on Sunday, the Workout Day and Home Run Derby on Monday, the Red Carpet Show and the All-Star Game itself on Tuesday, and the FanFest throughout the period.
"In '73, you flew in, you watched the game and you got out," Selig said. "Not today. You're going to be amazed by FanFest and the Home Run Derby. What it is, is a celebration of baseball, and it just gets bigger and bigger and bigger. It'll be 39 years at that point, but it'll be worth the wait."
Among the benefits to the Royals, he noted, was that the All-Star Game helps a team sell tickets during the regular season because season-ticket holders have access to purchase tickets to the Classic.
This year's game will be in Anaheim, and the 2011 game is scheduled to be played in Phoenix.
There was a momentary dash in Kansas City's hopes last year when a report surfaced that Boston wanted the 2012 game to help celebrate the 100th anniversary of Fenway Park. But Boston had the game as recently as 1999, when there was a memorable tribute to the Ted Williams, and Kansas City's hopes were realized Wednesday.
"They had a very interesting reason, which was the 100th anniversary," Selig said, "but here's Kansas City, who spent a lot of money fixing the stadium up, and it's remarkable. ... It was tough, but the Royals made a terrific presentation, and Mr. Glass is always very persuasive with me."
Selig was at the 1973 game in Kansas City as owner of the Milwaukee Brewers, and he reminisced about his friendship with Royals founder Ewing Kauffman.
"There was some concern about this game being played, and it finally was, and I also remember that Ewing threw quite a party that night at his home. Funny that I remember that 37 years later," Selig said.
They remained close over the years, working on various committees in baseball.
"In '93, I think, I was the last person in baseball to see him alive, and we had a very emotional meeting. I had just become acting Commissioner and I had a wonderful relationship with him," Selig said.
"I know it's a great day here, but [it's] a great day for baseball and, frankly, it's a great day for me."
David Glass was revved up about the return of the All-Star Game to Kansas City.
"I was here in 1973 and I can't wait for the next one," he said.