Fleischer said he had told the President last week that he was to leave, most likely in July, after facing the media as Bush's spokesman since he came to office in January 2001.
Fleischer -- nicknamed His Master's Voice -- said that President Bush ended their conversation over his resignation "by kissing me on the head".
Fleischer said his immediate plans are to help Bush get re-elected. "This is a wonderful job. I love this job, I love President Bush, I believe deeply in the policies and the man. But there comes a time in public service when you have to know when it is time to go.
"I really want to unwind, do something more relaxing, like dismantle live nuclear weapons," he said.
Reports suggest that he could be replaced by deputy press secretary Scott McLellan.
The New York Post reports that Fleischer, who married six months ago, was keen to leave his job before Bush's re-election campaign gets under way. The next presidential elections will take place in November 2004, but campaigning is already beginning.
The paper also claims that while Fleischer clashed with some of the President's aides, the resignation was his idea.
Fleischer has been a controversial figure with the media throughout his tenure at the White House, which has covered the 9/11 attacks, the subsequent invasion of Afghanistan and this year's war against Saddam Hussein's regime in Iraq.
He walked into a storm of controversy post 9/11 by suggesting that comments made by US comedian Bill Maher should not have been made, drawing criticism that he was not an advocate of freedom of speech.
More recently Fleischer has been accused of having a loose relationship with the truth.
Last week, he said that White House relations with Saudi Arabia were excellent, just before it was admitted the two governments had clashed over terror warnings.
When President Bush, a former National Guard pilot, did his 'Top Gun' stunt and piloted a US Navy S-3B Viking fighter as it landed on the aircraft carrier USS Abraham Lincoln, the White House spokesman claimed Bush had to use the combat aircraft rather than his helicopter because the warship was hundreds of miles offshore.
In reality, the ship was just 39 miles off shore. Democrats accused the president of a electoral PR stunt.
Other prospects to replace Fleischer include Ed Gillespie, a strategist, and Victoria Clarke, spokeswoman for the Pentagon.
Before joining the White House, Fleischer was as press secretary for Senator Pete Dominici from 1989 to 1994, following which he became spokesman for the House Ways and Means Committee. Prior to joining Bush's presidential campaign late in 1999, Fleisher was communications director for Elizabeth Dole, who was running to win the nomination as the Republican candidate for President.
Fleischer's departure is announced just as the creator of the fictional White House of the hit NBC television show 'The West Wing', Aaron Sorkin, pens his final script for the show. While the first two series of the show were immensely popular, the present series has seen ratings fall.
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