Sunshine on Leith star Kevin Guthrie took advantage of the 29-year-old woman who had appeared unwell after a night out.
The incident occurred at the Glasgow flat of fellow actor Scott Reid – Methadone Mick in BBC's Still Game.
Guthrie, 33, had insisted he had only “helped” the woman that night – but his DNA was found on the inside of her underwear.
The predator was found guilty of sexual assault at Glasgow Sheriff Court after denying the charge.
The attack occurred between September 30 and October 1 2017.
Guthrie, of the city's Yorkhill, appeared at court backed by a crowd of supporters.
He showed no emotion as he was locked up and put on the Sex Offenders’ Register for an indefinite period.
Sheriff Hughes said: “You had an educational background and worked extremely hard to get a part in acting in acclaimed films.
“The court must show that women can be protected from domestic sexual offences and those who do should suffer serious consequences.
“The offence you have been convicted caused distress and consequences to the young woman involved in this case.
“You committed this crime in a position of trust.
“She was unwell and thought her drink had been spiked elsewhere that night.
“The other man was urgently getting medical assistance and you were left in the room with her when she was not able to look after herself.
“The jury accepted that you committed these heinous crimes and the only appropriate sentence is imprisonment.”
The trial was told the woman had been due to meet Guthrie and Scott at a bar on the night of the alleged attack.
But Scott received a call from a taxi driver to collect her as she appeared ill.
He and Guthrie helped the woman into the flat in Glasgow's Kelvindale and put her on a bed.
Scott called NHS 24 leaving Guthrie in the room “to make sure she was OK”.
But, the woman recalled Scott not being in the room and bed covers then “being moved down my body”.
She went on: “I remember my top being lifted up and my bra being held down.”
The woman was groped by Guthrie before he performed a sex act on her.
She went on: “There would be times when Scott would come back in the room and he would pull the covers back on top of me and pull my top down.”
Guthrie – who also starred in the Fantastic Beasts film and Netflix series The English Game – carried out a further two sexual acts and kissed her on the mouth.
He would stop when Scott would come into the room.
She added: “I was unsure about what was happening, I could not believe it was happening.”
Prosecutor Harry Findlay asked why she did not say anything.
She replied: “I couldn’t...I found it difficult to communicate in any way.
“I think I was frozen as well.”
Guthrie refuted the accusations agreeing with his QC Gordon Jackson that it had instead been a “panic situation” due to the woman's condition.
However, his DNA was found on the inside of the woman’s underpants.
Mr Findlay asked Guthrie to explain why this was.
He said: “I can’t for the life of me explain in any rational sense how that happened.”
Gordon Jackson QC, defending, told the sentencing that Guthrie maintains his innocence.
The lawyer added: “If ever there was a case where something appears out of character it is this.
“This was a man who knows success, things can go to your head but he has been a decent composed individual.
“The price he will pay will be with his own career is immense.
“He wasn't a jobbing actor, he was doing well.
“No disrespect but no matter what you do to him, this will have an effect on his future and career.”