The legal team of the convicted Australian spy James Ricketson submitted an application to the Cambodian monarch, King Norodom Sihamoni, in search of a royal pardon, says his lawyer Kong Sam Onn.
He told AAP on Friday he submitted the request through the office of Prime Minister Hun Sen, which was expected to be sent to the monarch after a ministerial review.
The request followed a decision by the Australian filmmaker not to appeal his conviction and his six-year jail sentence after a marathon trial that was widely criticized by human rights groups and prompted clemency requests from Australian politicians.
"I submitted the letter of pardon to the prime minister's cabinet on Thursday, and the cabinet has already asked the Ministry of Justice to review the letter," said Kong Sam Onn.
Ricketson was convicted on August 31 of espionage and crimes that endanger Cambodia's national security under article 446 of the National Penal Code.
He was arrested 15 months earlier after flying an unmanned aircraft without a permit over a political rally organized by the now-opposition Cambodia National Rescue Party (CNRP).
Prosecutors alleged that Ricketson, 69, was spying for "foreign states," but declined to say which or called any witnesses to justify the charges.
He emphatically denied the allegations, but has since accepted the verdict.
"My father has decided to file a clemency request from the king, and the Australian government has indicated that they will fully support this presentation," his son Jesse said last week.
"This is no longer a legal issue but a humanitarian one, it's a matter of compassion and mercy, my father is an old man with health problems in incredibly difficult conditions."
Foreign Minister Marise Payne confirmed the Australian government's support for the request and said it welcomes the "Ricketson family's statement that Mr. Ricketson intends to formally file a clemency petition."
Under Cambodian law, a pardon can not be issued until the appeals process has been exhausted or eliminated. Normally it is requested by the condemned with the government then asking King Norodom Sihamoni for a real approval.
Ricketson has been held in miserable conditions in the prison of Prey Sar, where he has suffered numerous medical complaints including weight loss, scabies and lice, which led to his transfer to the prison hospital.
"Six years there they will kill him, we need to take him home, I, like his son, on behalf of his family and loved ones, I'm also asking for mercy personally so we can do it," Jesse said.