A Melbourne man has been sentenced to more than four years' jail for "terrorising" a young mother who he sexually assaulted as she slept next to her partner before stealing the family's car.

Lang Kouth entered a home at Cranbourne North in the middle of the night on July 24 this year in search of car keys.

After finding them, the County Court heard the intoxicated 21-year-old went into the couple's bedroom, where they were sleeping beside their baby, and got into bed next to the young mother.

Judge Michael Tinney said Kouth aggressively bit and kiss the woman on the neck, lips and face leaving her bruised.

"Not even her half-asleep resistance stopped you," he said.

"It's the stuff of nightmares. Your conduct will never be forgotten by those impacted by it."

When the woman realised a stranger was sexually assaulting her, she woke her partner and Kouth ran from the bedroom.

He stole the couple's car and then led police on a high-speed chase down the South Gippsland Highway before crashing into a tree.

Kouth pleaded guilty to aggravated burglary, sexual assault, theft, unlicensed and careless driving.

'She's got to live with that for the rest of her life'

Outside court, one of the victim's friends — who did not want to be identified — said she did not know if the young mother would ever be able to move on from the attack.

"She was terrorised … she's got to live with that for the rest of her life," she said.

"She sleeps in the lounge room because she doesn't want to go to the other end of the house.

"I can't fix what happened and I don't think anyone will ever be able to fix it."

The woman said her friend had been "bitten like a piece of meat" and called for increased jail terms for aggravated burglaries and sexual assault.

Judge Tinney said Kouth's prospects of rehabilitation were good if he sought treatment for his drug and alcohol issues.

Kouth will be eligible for parole in two years and three months.