John Conyers again denied the accusations, but said he was stepping down to clear his name.
Mr Conyers said that many of the allegations "were raised by documents reportedly paid for by a partisan alt-right blogger".
The files have not been independently verified by BBC News.
The leader of the Democrats in the House of Representatives, Nancy Pelosi, said it was imperative that Mr Conyers received "due process".
Ms Pelosi called him "an icon" who had advanced women's causes.