The 46-year-old married father of one who was in his second term in the House resigned within hours after the picture and e-mail messages appeared in a story on the Internet tabloid Gawker.com.
"It has been a tremendous honor to serve the people of Western New York," Lee said in a statement posted on his official House Web site. "I regret the harm that my actions have caused my family, my staff and my constituents. I deeply and sincerely apologize to them all.
"I have made profound mistakes and I promise to work as hard as I can to seek their forgiveness. I am announcing that I have resigned my seat in Congress effective immediately."
On Jan. 14, a 34-year-old Maryland woman's ad in the "Women for Men" section of Craigslist personal section looking for "financially & emotionally secure" men yielded a reply by a man using Lee's Gmail address and identifying himself as a 39-year-old divorced lobbyist who was "a very fit fun classy guy."
The woman responded to one of the initial messages and accompanying photos showing Lee in a blue polo shirt saying, "Are you sure that's not a photo from a J.C. Penney ad?"
The reply from Lee's e-mail address said: "Lol...no...Here...I just took one... I'm relaxing at home."
That photo was taken with a BlackBerry and showed Lee shirtless and flexing his muscles, Gawker.com said.
The woman reportedly ended the communications after determining Lee wasn't being truthful, then sent the material to Gawker, Lee and his wife Michele.
A spokesman for Lee initially told the Gawker the congressman's Gmail account had been hacked into Jan. 21.