The federal opposition will urge the government to make a plea for clemency if a former Australian soldier loses his death penalty appeal in Afghanistan.

Robert William Langdon, 38, has been convicted over the killing of an Afghan security guard in May last year.

Langdon, understood to have served as a Townsville-based infantryman, was employed by the US-based contractor Four Horsemen International as a security contractor at the time.

The government is providing Langdon with consular support and will seek to intervene in the case in line with its policy on any Australian citizen convicted of a capital offence.

The opposition is backing the government's action so far but wants it to go further if Langdon's appeal fails.

"We would hope the Australian government would support a plea of clemency for Mr Langdon," foreign affairs spokeswoman Julie Bishop told ABC Television on Thursday....