They had unprotected sex on his office desk, sent 6,000 filthy messages and discussed fetish outfits.
Just an hour after their first contact, the Rochdale member, 49, told the 22-year-old: “You’ve made me horny.”
Four days later they romped at his constituency office, for which he has received more than £22,000 in expenses this year.
The woman, whom was referred to as Alice, said: “He had me over his desk and was spanking me on the buttocks.
“He was sex mad.
“I felt quite privileged to be in there with such a well-known MP.
“It was quite a turn-on.
“Looking back, it was so irresponsible, he shouldn’t have been using his office as a sex pad.
“But I just went along with it because I fancied him.”
She said of the dad of four: “He was sex mad.”
She said: “He’s meant to be a respected pillar of the community but behaves like a horny teenager.”
Labour suspended Danczuk in December after he bombarded student Sophena Houlihan, 17, with sex messages.
Having sex at work could be viewed as gross misconduct, leading to immediate dismissal.
Alice explained how Danczuk gave her his mobile number after they began following each other on Twitter.
She told Danczuk she was still in her nightwear, prompting him to reply: “You’ve got my imagination running wild.
Four minutes later he added: “You’ve made me horny.”
He begged her to “tell me more”.
When she asked what about, he said: “About what we’re going to do when we meet.”
Alice answered: “It depends what you like.
“I’m a big fan of authority.
“Probably one of the reasons I find you so sexy.”
After agreeing to a date, he invited Alice to stay at his London flat and Spanish villa.
She said it “would be fun”, adding “Are you allergic to anything?”
When Danczuk, who was quizzed last year by police over an alleged historic rape, asked “No, why?” she admitted having “a big thing for latex”.
He said “Sounds incredibly interesting” and added he was “looking forward to meeting”.
Danczuk later messaged: “I will turn up at yours, we’ll f*** then we’ll go out, come back and f*** some more.”