The woman told Delhi Police that Rawat called her to his home in Green Park on Friday and raped her. Sources said she approached police on Friday night and registered a complaint.
Police sources said the woman had filed a similar case against Rawat more than 15 years ago.
Rawat was a prominent leader of a rebel MLA group that walked out of the Congress in Uttarakhand earlier this year, plunging the government into a crisis and prompting the Centre to clamp President’s Rule in the state.
But the Supreme Court scrapped the central rule and chief minister Harish Rawat won a crucial floor test in the assembly after the rebel legislators were disqualified from voting.
Harak Singh and the other rebels formally joined the BJP about two months ago.