Freshman Rep. Katie Hill, a rising Democratic star in the House, announced her resignation Sunday amid an ethics probe, saying explicit private photos of her with a campaign staffer had been "weaponized" by her husband and political operatives.
The California Democrat, 32, had been hand-picked for a coveted leadership seat.
But in recent days, compromising photos of Hill and purported text messages from her to a campaign staffer surfaced online in a right-wing publication and a British tabloid.
The House ethics committee also had launched an investigation into whether Hill had an inappropriate relationship with an aide in her congressional office, which is prohibited under House rules.
Hill, one of the few openly bisexual women in Congress, has denied that and vowed to fight a "smear" campaign waged by a husband she called abusive.
But her relationship with the campaign aide became a concern for House Democrats who have made equality in the workplace a particular priority.
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On Sunday, after apologising for the relationship with a subordinate, Hill announced she was stepping aside.
"It is with a broken heart that today I announce my resignation from Congress," she wrote in a statement released Sunday.
"Having private photos of personal moments weaponised against me has been an appalling invasion of my privacy. It's also illegal, and we are currently pursuing all of our available legal options," she added.
"However, I know that as long as I am in Congress, we'll live fearful of what might come next and how much it will hurt."
But Rep. Tom Emmer, R-Minn., chairman of the House GOP campaign arm, said Republicans "look forward to winning back this seat."
In a statement Sunday, Pelosi praised Hill for bringing "a powerful commitment to her community and a bright vision for the future" to the House but added: "She has acknowledged errors in judgment that made her continued service as a Member untenable. We must ensure a climate of integrity and dignity in the Congress, and in all workplaces."
"I can no longer allow my community, family, friends, staff, supporters, and especially the children who look up to me as a role model, to suffer this unprecedented brand of cruelty."
She apologised to "people who have been hurt."
While not providing any evidence of abuse, Hill says she turned elsewhere for companionship because of their turbulent relationship and lamented that "the deeply personal matter of my divorce has been brought into public view."