The former boss of Australia's special forces has been appointed as the head of the country's intelligence security service.

Duncan Lewis will take over the role of Director-General at the Australian Security Intelligence Organisation (ASIO) in September, a joint statement by the Foreign Minister and the Attorney General's offices announced.

"Mr Lewis brings a wealth of national security experience as well as sound judgment to this important role," the joint statement said.

"The Government has every confidence he will provide strong leadership to ASIO and sound advice on security matters."

Mr Lewis is currently serving as Australia's ambassador to Belgium, Luxembourg, NATO and the European Union.

He will be replaced in those roles by one of the Prime Minister's senior advisers, Dr Mark Higgie.

Mr Lewis rose through the ranks of the Australian military to the role of chief of special forces, before becoming the Federal Government's security advisor.

He was then appointed the Secretary of Defence before moving on to his current ambassador role.

Mr Lewis joins Australia's spy agency at a time of increased scrutiny over the organisation's budget, and a significant push into cyber-security.

The current head of ASIO, David Irvine, announced his retirement earlier this year and will officially hand over the reigns of the spy agency to Mr Lewis on September 15.