Matthew Hancock preyed upon the victim at a house in Leeds as she drifted in and out of consciousness due to the effects of drugs and alcohol.
Hancock was found guilty of the offence by a jury at Leeds Crown Court after a trial in which he gave evidence and accused his victim and another woman of making up the allegation as part of a "conspiracy."
The court heard Hancock, the victim and the woman had been drinking alcohol and smoking cannabis on the night of the attack.
During the course of the evening the victim felt unwell and vomited before laying down on a sofa.
Hancock carried out the offence when the other woman briefly left the room.
The defendant slapped the woman across the face and lifted her arms to check if she was unconscious before carrying out the assault.
He stopped the assault as the other woman returned to the room.
Police were contacted after the victim rang her boyfriend and the other women to tell them what Hancock had done.
Hancock, 28, of Windmill Lane, Batley, was found guilty of assault by penetration.
The defendant claimed during the trial that the two women had made up the allegation against him for flirting with another woman earlier in the evening.
Prosecutor Richard Woolfall read a statement to the court on behalf of the victim describing the trauma she had suffered since the offence.
She said: "I am no longer the same person.
"I am no longer able to relax in any situation.
"My ability to trust has gone.
"I don't know if I will ever trust a man again."
The woman also described how she had been given medication to cope with the ordeal.
A pre-sentence report stated Hancock now admits carrying out the offence.
Charles Blatchford, mitigating, said Hancock has no previous convictions for sexual offences.
The Judge, Recorder Abdul Iqbal QC, told Hancock he must serve two-thirds of the seven-year sentence in custody before he can be released on licence.
He said: "The jury rejected your defence that it was a conspiracy to incriminate you for a serious offence."
"The impact upon the complainant has been very significant indeed."