The body of missing Australian soldier Paul McKay has been found near the summit of Scarface Mountain in upstate New York, 15 days after he was last seen alive.

An autopsy on the body of the Canberra soldier completed in the US on Thursday found he died of an irregular heartbeat due to hypothermia. Essex County Coroner Francis Whitelaw ruled the manner of death to be suicide.

Captain McKay was suffering post-traumatic stress disorder after a tour of Afghanistan and was on leave from the Australian Army.

Saranac Lake police chief Bruce Nason said Captain McKay's Australian family had been notified.