The former leader of the US Republican Party in the House of Representatives, Tom DeLay, has said he will not seek re-election to the body in November.
Mr DeLay has said he will continue working for the Republican cause
The 58-year-old has been accused of laundering corporate contributions for use in Republican campaigns in Texas.
He has strongly denied the charges in a case which has yet to go to trial.
Mr DeLay said he did not want the Democratic Party to steal his seat "with a negative personal campaign" in November's mid-term polls.
In a videotaped statement, he said his "love for the Republican Party has played no small part in this decision".
He did not want the campaign for his House seat to be "focused solely as a referendum on me", he added.
"After many weeks of personal, prayerful thinking and analysis, I have come to the conclusion that it's time to close this public service chapter of my life."
Officials close to Mr DeLay have said he is likely to leave Congress by the end of May or mid-June.
'Continue to fight'
Correspondents say Democrats have sought to portray Mr DeLay as the face of what they deem a "culture of corruption" within the Republicans, as they campaign to win back control of Congress.
In an interview with US weekly magazine, Time, published on Monday, Mr DeLay said he did not want to risk his seat.
"I can do more on the outside of the House than I can on the inside right now," he said.
"I want to continue to fight for the conservative cause. I want to continue to work for a Republican majority."
Last week Mr DeLay's former deputy chief of staff pleaded guilty to corruption, saying he ran a criminal enterprise while working for the politician.
Mr DeLay's decision to quit throws the spotlight on Republican Party corruption in a manner which will do the party no good, the BBC's Justin Webb reports from Washington.
The White House is not directly involved, although late last year President George W Bush said he believed Mr DeLay was innocent of any wrongdoing.
Mr Bush may now regret his decision to be so supportive, our correspondent says.