Emergency Services Agency Commissioner Mark Crosweller told staff via email that he was giving up the leadership of the territory's ambulance, fire, and volunteer emergency services.

He has resigned to take up a position as the the director-general of Emergency Management Australia, a federal agency with a coordinating and strategic policy role.

The commissioner's departure leaves the top job open as the ACT approaches the summer bushfire season.

But Mr Crosweller told The Canberra Times the timing of his resignation would in no way compromise the city's preparedness for natural disasters.

He said it had been "a great honour and a privilege' to lead the ACT's emergency services for the past three years.

"I was very happy in the territory, I'm not leaving because I was unhappy," Mr Crosweller said.

"Having spent pretty much my whole life adult life in emergency services and emergency management, it's just a great honour to work at the national level," he said.

He will be temporarily replaced by the head of the State Emergency Service, Chief Officer Tony Graham, until the position can be filled permanently.

Mr Graham has 20 years involvement with the SES, a career that has included leadership roles in some of Australia's worst disasters.

He led SES officers during the Thredbo Landslide of 1997 and the the Victorian Bushfires in 2009.

The hunt for a new commissioner will begin almost immediately, with the Justice and Community Safety Directorate planning to advertise the role in national media tomorrow.

Mr Crosweller was first appointed as head of emergency services in January 2010, coming from the NSW Rural Fire Service, where he was Assistant Commissioner.

He helped move the ESA headquarters to Fairbairn, forge better relations between the various services, and strengthened the city's bushfire preparedness significantly.

He also continued the maturing of the city's fire, ambulance, and volunteer services since the devastating 2003 bushfires.