Governor-General Peter Cosgrove has appointed NSW Governor Marie Bashir as his deputy.

NSW Governor Marie Bashir has been formally appointed deputy to Governor-General Peter Cosgrove.

The role of deputy by convention goes to the longest-serving state governor in the country.

But Ms Bashir will only hold the role until September, when she is due to retire after 13 years in the job.

With the retirement of governors in Queensland and South Australia this year, the role will fall to Tasmanian Governor Peter Underwood.