A man has been sentenced to 12 months in prison for illegally marrying a 14-year-old bride in an Islamic wedding in Melbourne last year.

The Burmese asylum seeker was handed a maximum sentence of 18 months but was given a 12-month release date.

He has already spent nearly a year in custody so will be returned to immigration detention indefinitely on his release in a fortnight.

The man cannot be sent back to Myanmar as he is a member of persecuted minority.

It is the first prosecution in Australia under the laws since they were established in 2013.

Judge Lisa Hannan told the man he clearly knew what he was doing was wrong.

"You knew what you were doing was contravening the law of this country and proceeded in the face of advice to that effect," she said.

"I must seek to deter not only you, but others who might engage in like conduct."

The man, aged in his 30s, had pleaded guilty to going through a formal ceremony of marriage with a person not of marriageable age at Noble Park last September.

He and his bride cannot be identified for legal reasons.

At a pre-sentencing hearing on Wednesday, the man's defence lawyer, Sophie Parsons, said the girl's mother had been behind the wedding.

Ms Parsons told the court the girl had been having difficulties with her stepfather and her groom saw himself as "rescuing the [girl] and becoming the supportive figure in her life".

The man cried during most of the pre-sentencing hearing and was in tears in court again today.

Ms Parsons said the man, who became friends with the bride when he was living as a boarder in the same house as her, was "culturally isolated".

The man was living in Melbourne on a bridging visa at the time of the wedding.

He was vulnerable to the reassurances of the girl's mother and the imam that married the pair, Ms Parsons said.

The imam, Ibrahim Omerdic, was later convicted and jailed for two months for his role in the illegal ceremony.

He was filmed telling the couple he could not give them a copy of the marriage certificate as the girl was "very young".

On footage played during the court proceedings, Omerdic could be heard confirming the man had handed over $1,480 worth of gold as a traditional form of payment to the bride's family.