Samuel Armstrong, an aide for South Thanet MP Craig Mackinlay, is alleged to have "abused his position" by attacking the woman after drinking with her at a bar in the Palace of Westminster.
Armstrong is accused of "taking advantage" of his alleged victim, who is in her 20s, when she fell asleep as they were alone in the office of the Tory MP, Southwark Crown Court heard.
The 24-year-old played jazz music, then started kissing and touching the woman before asking her back to his flat, jurors were told.
The court heard that when she told Armstrong "no", he repeatedly called her a "b****" before taking off her clothes and assaulting her.
Armstrong, of Danbury in Essex, denies two counts of rape, one of sexual assault and one of assault by penetration on 14 October last year.
The defendant claimed in a police statement he gave shortly after being arrested that what took place happened with "full consent", the court heard.
Prosecutor Mark Heywood QC said he raped her twice, abusing "his role and his position".
"She, in distress, walked and ran through the corridors of Westminster, eventually finding and telling cleaning staff what had happened," he said.
"He went out another way, using his pass and sending her messages, one of which suggested that he was concerned and that she contact him if she had 'any issues'."
The jury was told that on the day in question, Armstrong and the woman were drinking with others at the Sports and Social Bar.
Then, at around 9.40pm, they went to the roof garden terrace so she could look at Big Ben, before going back to the bar.
She said she had consumed four or five drinks but did not think she was "tipsy", describing the mood as "very jolly" and "playful".
Around the time of last orders, Armstrong and the complainant went to Mr Mackinlay's office, where the defendant played jazz music on a laptop, the court heard.
At this stage, neither looked particularly affected by drink, Mr Heywood said.
The pair sat and talked on a three-seater sofa, where she fell asleep, the court heard.
Mr Heywood said: "This time is where it began to go wrong, in the early hours. It is the prosecution case, the defendant took advantage of the situation and of her obvious and open friendliness towards him."
Armstrong started kissing and touching the woman, before asking her to come back to his flat in Clapham, south London, the court heard.
Jurors were told that when she mumbled "no" several times, the defendant's manner changed and he repeatedly called her a "b****".
She "froze" as he became "physical", taking off her clothes and assaulting her, the court heard.
Mr Heywood said the woman asked: "What are you doing?"
"This is what you want," Armstrong allegedly told her.
Mr Heywood said: "In saying that he was not, of course, genuinely speaking for her or reflecting any truth of the situation. He was imposing himself on her."
The woman was seen on CCTV running through the corridors of Westminster and leaving through Portcullis House just after 2am.
The trial, which is set to last for two weeks, continues.