Armstrong's return from cancer to win the Tour a record seven consecutive times made him a hero to cancer patients worldwide and elevated cycling to an unprecedented level in America.
The 36-year-old Armstrong told Vanity Fair in an exclusive interview posted on its Web site on Tuesday that he was inspired to return after finishing second last month in the Leadville 100, a lung-searing 100-mile mountain bike race through the Colorado Rockies.
"This kind of obscure bike race, totally kick- started my engine," he told the magazine. "I'm going to try and win an eighth Tour de France."
The sport and particularly the Tour have missed his star power, even though skeptics refused to believe he could win seven Tours without the help of illegal performance-enhancing drugs.
The 2009 Tour "is the intention," Armstrong's spokesman Mark Higgins told The Associated Press, "but we've got some homework to do over there."
Tour director Christian Prudhomme did not return messages seeking comment on Armstrong's decision.
In a video statement on his foundation's Web site, Armstrong said details -- such as a team and schedule -- will be announced Sept. 24 at the Clinton Global Initiative in New York City.
"I am happy to announce that after talking with my children, my family and my closest friends, I have decided to return to professional cycling in order to raise awareness of the global cancer burden," Armstrong said in a statement released to the AP. "This year alone, nearly eight million people will die of cancer worldwide. ... It's now time to address cancer on a global level."
In the Vanity Fair interview, Armstrong told the magazine he's 100 percent sure he's going to compete in the Tour next summer.
"We're not going to try to win second place," Bill Stapleton, Armstrong's lawyer and longtime confidant, told the AP.