Weiner staffers have already cleared out of their Washington, D.C. offices, locking the door behind them.
Weiner told friends he would step down after a torturous, three-week stretch during which his perverse self-portraits and sordid sexts to online female friends were revealed, sources said.
Word that Weiner was quitting came as top Democrats were preparing to turn the screws and strip him of his committee assignments.
Weiner had previously indicated he wanted to speak with his pregnant wife, Huma Abedin, before making his decision. She returned to their Washington, D.C., home Wednesday after an international trip with Secretary of State Hillary Clinton.
Evidently, they came to a decision about Weiner's political career. It remains to be seen whether their 11-month-old marriage survives.
Weiner notified House Minority Leader Nancy Pelosi and Rep. Steve Israel, chairman of the Democratic Congressional Campaign Committee, on Wednesday night by phone while they were at a White House picnic.
Pelosi told Weiner they were planning to strip him of his committee seats Thursday and "basically said they would not rest until it was done," a Democratic source said.
Weiner is undergoing treatment for his sexual problems and is on a two-week leave from Congress.
Weiner, 46, was under massive pressure to step down after his kinky computer antics and repeated lies turned him into a political pariah and a late-night punchline.
The scandal began after Weiner accidentally sent out a crotch shot via Twitter - which was followed by an increasingly appalling series of nude and semi-nude photos of the congressman.
Every day seemed to bring a new indignity, from President Obama's rebuke to a porn star going public with word that Weiner had asked her to lie about their cyber-relationship.
The Democrat - once considered a front-runner in the race for City Hall - finally came clean at a tearful news conference where he acknowledged wooing a half-dozen woman via Twitter, Facebook and text messages.
The creepy congressman even exchanged Facebook messages with a 17-year-old high school girl from Delaware. Those turned out to be G-rated.
Complicating the mess was word that his wife was pregnant with their first child. Abedin has not yet commented publicly on her husband's humiliation.
With Larry McShane