WASHINGTON—Rep. John Conyers, the longest-serving curent member of the House of Representatives, resigned from Congress on Tuesday, after facing calls to step down over allegations of inappropriate behavior toward female staff members.

Multiple former staffers have accused the Michigan Democrat in the past two weeks of sexual misconduct. Both House Speaker Paul Ryan (R., Wis.) and House Minority Leader Nancy Pelosi (D., Calif.) called on Mr. Conyers to resign last week, putting pressure on the Detroit-area lawmaker first-elected...