A Sydney priest who used a webcam to broadcast himself masturbating to a person he believed was a 13-year-old girl will be behind bars for at least six months.

Robert MacGregor Fuller, 54, has been sentenced to a maximum of 18 months in jail for grooming and procuring a child under the age of 16.

However Fuller was given a six-month parole period and six months off his sentence for an early guilty plea.

During online chat sessions, the priest who served for some six years at All Saints church in the Sydney suburb of Liverpool, used a webcam to show himself masturbating to a police officer posing as a 13-year-old girl.

Judge Allan Hughes told Parramatta District Court that Fuller knew what he was doing was wrong and expressed that in his conversation with the assumed 13-year-old girl.