"During my time in Congress, I have always acted in an ethical manner within the rules of our body and the laws of our land," the Texas lawmaker told fellow Republicans in a letter informing them of his decision.
Still, referring to criminal charges he faces in his home state, he added, "I cannot allow our adversaries to divide and distract our attention."
DeLay temporarily have given up his leadership post after he was charged, but always insisted he would reclaim his duties after clearing his name.
His turnabout cleared the way for leadership elections among Republicans buffeted by poor polls and by lobbyist Jack Abramoff's confessions of guilt on corruption charges in connection with congressional wining and dining.
Earlier this week, former House Speaker Newt Gingrich told the CBS Evening News that
"As a practical matter, he can't go through this whole process and be an effective leader," Gingrich said.
Speaker Dennis Hastert, his own grip on power secure, said he expects elections to be held when lawmakers return to the Capitol the week of Jan. 31. That set the stage for several weeks of political maneuvering, and the possibility of a wholesale shuffle in the leadership lineup 10 months before midterm elections.
There's no shortage of candidates lining up to replace DeLay, but there is no one else like him – a brash, often-uncompromising conservative, reports CBS News correspondent Gloria Borger.
Democrats, eager to take control of the House in November, reacted to DeLay's announcement with studied indifference.
"The culture of corruption is so pervasive in the Republican conference that a single person stepping down is not nearly enough to clean up the Republican Congress," said Rep. Nancy Pelosi of California, the Democratic leader.
Added Rep. Rahm Emanuel of Illinois, chairman of the House Democratic campaign organization: "With the permanence of their special interest philosophy, a change in the Republican cast of characters simply doesn't matter."
Democrats must gain 15 seats in November to win control of the 435-member House.
Missouri Rep. Roy Blunt, the GOP whip who has been acting as majority leader while DeLay fights his own legal battle, signaled he intends to run for majority leader.
Ohio Rep. John Boehner, once a member of the leadership, was expected to make a formal announcement on Sunday.
One official, speaking on condition of anonymity, said DeLay called Hastert, R-Ill., on Saturday to inform him of his decision. "Our success in lowering taxes, creating jobs, growing the economy and providing effective national security was helped by Tom Delay's leadership," the speaker said in a statement.
The 58-year-old DeLay, an exterminator before his election to Congress in 1984, said he intends to seek re-election next fall. "I plan to run a very vigorous campaign and I plan to win it," he told reporters in Texas.
The voters aside, his political future will hinge not only on the outcome of the Texas allegations, but on the future of the Abramoff investigation.
Michael Scanlon, a former DeLay aide and an Abramoff business partner, pleaded guilty in the fall to corruption charges. In court papers, the lobbyist said he had once paid $50,000 to the wife of another former DeLay aide to help kill legislation opposed by his clients.
DeLay has been a fixture in the Republican leadership since the GOP won its majority in the 1994 election landslide.
An outsider at first, he muscled his way up the hierarchy when he won election as whip over the hand-picked choice of then-Speaker Newt Gingrich, R-Ga.
When Gingrich nearly fell in a coup more than three years later, DeLay went before fellow Republicans at a private meeting and emotionally confessed his role in the plotting. He prospered politically, moving up to become majority leader, the No. 2 post, in 1999.
Contrition was never a quality he displayed to his adversaries — Democrats, outside interest groups and others who sought to check the advance of the conservative GOP agenda he promoted.
DeLay raised millions of dollars for the campaigns of fellow House Republicans, conservatives and moderates alike, earning their gratitude regardless of their ideology. He courted controversy almost reflexively, including his involvement in an attempt to force corporations and industry groups to hire more Republican lobbyists.
He rarely backed down.
DeLay was the driving force behind President Clinton's impeachment in 1999, weeks after Republicans lost seats at the polls in a campaign in which they tried to make an issue of Clinton's personal behavior.
DeLay's downfall began at home in Texas, when he led a drive to redraw the state's congressional district boundaries and increase the number of GOP seats in the U.S. House. He succeeded, but was soon ensnared in an investigation involving the use of corporate funds in the campaigns of Texas legislators who had participated in the redistricting.
Flashing his trademark defiance, DeLay attacked prosecutor Ronnie Earle as an "unabashed partisan zealot." He pledged repeatedly to clear his name and said he would reclaim his duties as majority leader by the end of January.
The scandal spawned by Abramoff intervened, though.
Within two days of the lobbyist's appearances in federal court last week, GOP lawmakers began circulating petitions calling for elections. Hastert immediately made clear he would not stand in the way.
`After the Abramoff thing we got critical mass," said Rep. Jeff Flake, R-Ariz., who long had advocated new leadership.
While Flake is a conservative in a safe congressional district, others suddenly calling for change were more moderate Republicans who could face difficult re-election campaigns this fall.
New Mexico's Heather Wilson was among them.
She said three of DeLay's "former senior staff members have admitted or have been implicated in corrupt and illegal activities to get money for themselves by influencing legislation. Whether or not Mr. DeLay was involved himself or knew this was going on, he is responsible for his office."