Samuel Keegan, 29, of King Street, attended the BP service station on Warrnambool's Raglan Parade shortly after midnight on December 9 last year.

When a lone female employee approached the front counter, Keegan rushed towards her brandishing a 24-centimetre kitchen knife.

He was wearing a green hooded jumper over his head and a zombie costume mask on his face.

Keegan said if the victim gave her "all the cash" nothing would happen.

The terrified employee handed over $190 cash and the man left the store.

Keegan pleaded guilty in Warrnambool County Court on Thursday to armed robbery.

The court heard police arrived at the service station at 12.15am to find the victim visibly shaken and frantic.

Keegan's distinctive voice and walk was identified by police who viewed CCTV footage of the robbery.

He was arrested at 10.15am and a subsequent search warrant uncovered the knife, distinctive green jumper and majority of the cash.

In a police interview, Keegan said he'd consumed a whole bottle of whiskey that night and was sound asleep at the time of the offending.

He said he didn't recognise the man on the CCTV footage and the items located at his home were a coincidence.

But on Thursday, Keegan told the court he was "truly, truly sorry", that there wasn't a day he didn't think about the offending and he was willing to accept the consequences.

At the time of the offending the man was on two community correction orders.

He has a lengthy criminal history involving dishonesty offending and an aggravated burglary.

The man's lawyer conceded the offending was a serious example of an armed robbery on a soft target.

She said at the time of the offending Keegan was in a highly emotional state due to a relationship break-down and was struggling to survive after losing his job due to COVID-19.

She said Keegan was heavily intoxicated and affected by cannabis.

The court heard the man was diagnosed with bipolar disorder and autism spectrum disorder.

Keegan's lawyer said he had also suffered significant childhood trauma.

The man will be assessed for community correction and justice orders.

It is expected the assessments will take up to 12 weeks.

He will be sentenced at a later date.

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