Authorities warned a Melbourne mother and her 14-year-old daughter's groom-to-be that it would be illegal for the pair to marry just a day before they went ahead with an Islamic wedding, a court has been told.

A Burmese asylum seeker sobbed through a pre-sentencing hearing in the County Court in Melbourne after pleading guilty to marrying the girl at a Noble Park mosque last year.

The man in his 30s cannot be named due to a court-issued suppression order to protect the identity of the high school student.

The court was told the man was living as a boarder in the same house as the girl when they struck up a friendship.

Prosecutor Krista Breckweg told the hearing that a day before the marriage ceremony, Department of Health and Human Services (DHHS) workers warned the girl's mother and the man that it would be illegal for them to marry because the girl was under 16.

"This offender turned his nose up at what DHHS was saying to him," she told the hearing.

"He clearly knew it was wrong, it's not a case of cultural misunderstanding."

Groom thought he was 'rescuing' girl: lawyer

But the man's defence lawyer, Sophie Parsons, said the girl's mother had been the principal organiser of the union.

"The complainant's mother raised the idea on several occasions with [her daughter] and then reassured and encouraged my client to proceed with the marriage ceremony," she told the hearing.

She said the girl had been having difficulties with her stepfather and her groom-to-be saw himself as "rescuing the [girl] and becoming the supportive figure in her life".

Judge Lisa Hannan said the girl's mother was lucky she had not been charged as a co-offender.

The man was living in Melbourne on a bridging visa at the time of the wedding, having fled Myanmar as an asylum seeker.

Ms Parsons told the hearing the man was "culturally isolated" and was vulnerable to the reassurances of the girl's mother and the imam that married the pair.

"He understands very clearly there is a different culture here," she said.

But Judge Hannan said it was not a cultural issue, but a legal one.

"He's warned in close proximity, he's warned he cannot do that by an Australian authority," she said.

Girl 'too young' for marriage certificate: imam

Police found a video of the wedding ceremony on the man's phone when he was arrested five days later.

It showed the pair in the office of imam Ibrahim Omerdic, who was later convicted and jailed for two months for his role in the illegal ceremony.

The court was told Omerdic could be heard confirming the man had handed over $1,480 in gold as a traditional form of payment to the bride's family.

The disgraced former imam could also be heard telling the couple he could not give them a copy of the marriage certificate as the girl was "very young".

The court was told the man will be released to immigration detention when he serves his jail term.

He cannot be sent back to Myanmar as he is a persecuted minority.

The man faces a maximum five years' jail and will be sentenced in the County Court.