Kasten told the Nationals a year ago that he was leaving the club after the season, but didn't make the announcement until Thursday afternoon. He did not say what he is going to do after his departure, and it is not known who will replace Kasten in Washington.
There have been reports over the past few years that he would work for the Blue Jays, Cubs or Major League Baseball, but he has denied those reports. Kasten was also a successful GM with the Atlanta Hawks of the NBA.
As of now, Kasten will still have an ownership stake in the club. It's not known what he will do with his shares.
"I really shouldn't talk about the next step," Kasten said.
Kasten, who joined the Nationals as the club president in 2006, said he is not leaving because of philosophical differences with the Lerner Group, although published reports have said otherwise.
"This has nothing to do with anybody else," an emotional Kasten said. "This is just about me -- what's good for me and my family and my own personal expectations, goals and aspirations. It's purely that. Nothing else. Will I miss things? You bet. There will be so much that I will miss."
Principal owner Mark Lerner indicated there was nothing wrong between Kasten and the Lerner Group. In fact, Lerner called Kasten "a great colleague and dear friend."
"He will always be a part of this organization," Lerner said. "His decision to back away from the day-to-day duties is understandable and was not a surprise. He gave us 24-hours-a-day for five years and will always have our respect, loyalty and friendship. He has promised to never be further than a phone call away, and we intend to keep him on speed-dial."
Kasten vowed to improve the team's depleted farm system during his first news conference in May 2006, and he made good on the promise as the Nationals went from having one of the worst farm systems in baseball to a respectable one, thanks to strengthened scouting and player-development teams.
With Kasten's help, general manager Mike Rizzo hired assistant GM Roy Clark, special advisor Ron Schueler, scouting director Kris Kline and player procurement director Kasey McKeon.
The system is now loaded with pitchers -- including 2009 No. 1 overall Draft pick Stephen Strasburg, who is recovering from Tommy John surgery -- who are expected to make an impact in the big leagues very soon.
The team also has its share of sluggers in the system including Bryce Harper and Michael Burgess. Both players are expected to be in the big leagues in two years.
"You know I feel great about how far we have come and the platform we now sit on for the future," Kasten said. "I want to go into a lot more detail as soon as the season is over, and I will. I think now is not the time for the global assessment. I just want to get this news [of my leaving] out of the way. Let's get back to the team.
"I think we are really poised to take off. I think we have ownership that is really ready to take the next step. We talk about it a lot. I have a level of confidence that it's going to happen."
Kasten said he doesn't have a crowning achievement during his time with the Nationals until they win a World Series championship. The team never had a winning season under Kasten, but managing principal owner Ted Lerner feels Kasten did a lot for the franchise.
"Over his tenure, he has positioned the Nationals to become one of the most exciting franchises in baseball and we thank him for all that he has accomplished," Lerner said in a statement. "We certainly respect his decision to pursue other interests at the end of the regular season, but will continue to call upon him for his vast knowledge of the game, the league and the franchise. He will remain a friend and valued partner of the team and ownership group."
Kasten came to the Nationals after a successful run as president of the Braves. It was Kasten who hired Bobby Cox to be manager of the Braves and the club went on to win 14 straight division titles, five pennants and one World Series.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.