"I'm here today to again apologize for the personal mistakes I have made and the embarrassment I have caused," he said reading from a brief statement in Brooklyn.
"I make this apology to my neighbors and my constituents, but I make it particularly to my wife, Huma."
Weiner's wife was absent as he announced his decision, as she was 10 days ago when he admitted having sent inappropriate messages and photos to several women online.
Weiner said he had hoped to remain in Congress but conceded his predicament had made that impossible. Instead, he said he would resign "so my colleagues can get back to work, my neighbors can choose a new representative and, most importantly, that my wife and I can continue to heal from the damage I have caused."
In part, that echoed what party leaders have said for days as they pressured him to resign so Democrats could resume positioning themselves for the 2012 election campaign without constant criticism from Republicans on moral grounds.
Weiner made his announcement at the same senior citizen center in Brooklyn where he announced his candidacy for the New York city council in 1992. He did not take questions, leaving unsaid whether his resignation from Congress marked an end to his career, or perhaps an ignominious pause for a brash liberal with ambitions to become mayor of New York.
The crowd on Thursday included hecklers and radio shock jocks, vying for attention at what became a New York media event.
Weiner, 46, has been on leave from the House since last weekend. He had not been seen in public since telling reporters on Saturday morning he intended to return to work.
One official said Weiner telephoned House Democratic leader Nancy Pelosi and Rep. Steve Israel of New York, the head of the party campaign committee, on Wednesday evening to tell them of his plans to quit.
They had pressured him to resign, concluding the relentless media focus on his activities was complicating the Democrats' efforts to position themselves politically for the 2012 elections.
Weiner's decision to give up his House seat marks the end of a nearly three-week sex scandal without the sex - an event that resulted from the brash New Yorker's use of social media such as Twitter and Facebook.
He at first denied having sent any inappropriate photos, then recanted in a remarkable news conference 10 days ago at which he admitted having exchanged inappropriate messages with several women.
His confession triggered a tabloid-style frenzy in print and online that only grew more pronounced a few days later when an X-rated photo surfaced on a website.
After initially calling for a House ethics committee investigation, Pelosi dramatically ramped up the pressure on Saturday when she joined with Israel and Rep. Debbie Wasserman Schultz of Florida, leader of the Democratic National Committee, in calling on Weiner to step down.
Within hours, Weiner disclosed his plans to enter treatment, and Pelosi's aides made it known that did not negate her demand for a resignation.
President Barack Obama added to the pressure on Monday, saying it he were in Weiner's situation, he would step down.
Several officials have said in recent days that Weiner was reluctant to make any decision about his career without speaking with his wife, a top aide to Secretary of State Hillary Rodham Clinton who had been overseas since shortly after the scandal broke. The trip ended Tuesday night.
Abedin is pregnant with the couple's first child.
Weiner's outspoken, in-your-face style cheered liberal supporters and angered conservatives. He even irritated some party leaders in 2009 when he led the charge for a government-run health care system long after the White House had made it clear that Obama was opposed.
Weiner's district includes parts of Queens and Brooklyn. New York Gov. Andrew Cuomo has the authority to call a special election to fill the seat once the congressman submits his resignation.
Weiner's political problems began on May 28 when BigGovernment.com, a website run by conservative commentator Andrew Breitbart, posted a lewd photograph of an underwear-clad crotch and said it had been sent from Weiner's Twitter account to a Seattle woman.
Initially, Weiner lied, saying his account had been hacked. But he pointedly did not report the incident to law enforcement - a step that could have led the way to charges of wrongdoing far more serious than mere sexting.
Additionally, his public denials were less than solid - particularly when he told an interviewer that he could not "say with certitude" that he wasn't the man in the underwear photo.
Still, the congressman said he had retained an attorney and hired a private security company to figure out how someone could pull off such a prank.
Weiner entered politics as an aide to then-Rep. Chuck Schumer, who represented parts of Brooklyn.
Now a senator, Schumer was one of only a few senior party leaders who refrained from calling publicly on his protDegDe to quit as the furor enveloped him in recent days.
Weiner served on the New York City Council from 1992 until his election to the House in 1998, taking over the seat vacated by Schumer when he made his successful Senate bid.