A Muslim cleric has been charged in Sydney over the alleged illegal marriage of a 13-year-old girl earlier this year.

The 35-year-old was arrested outside Parramatta Police Station yesterday afternoon.

The cleric, from the Hunter region, has been charged with solemnisation of a marriage by an unauthorised person.

He has been released on strict bail conditions and is due to appear in Parramatta Local Court in April.

The marriage has no legal standing in Australia because of the girl's age.

A 26-year-old Lebanese national remains in custody after being charged last week with child sex offences.

Police say he met and married the 13-year-old girl in the Hunter region, where he allegedly began a sexual relationship with her.

The man and girl then moved to Sydney's west earlier this year.

The relationship came to light when the man tried to enrol the girl at a high school.

Police also questioned the girl's parents last week and said they believed the parents had a hand in arranging the marriage.

Detective Inspector Peter Yeomans from the Child Abuse Squad said after today's arrest that more charges may still be laid in the months ahead.

"We're still investigating the matter, it's only early days. We only received the allegation on, I think it was last Thursday," he said.

"But there may be other persons charged or even further charges in relation to people who have already been charged in relation to this."

New South Wales Premier Barry O'Farrell has praised police for charging the cleric over the marriage.

"I'm delighted charges have been laid against the celebrant who allegedly solemnized this wedding that was clearly illegal," he said.

"We have rules in this country, in this state, about those who celebrate marriages, whether they are religious celebrants or civil celebrants.

"Those rules say that people have to be over the age of 18 unless a court has specified otherwise."