Bob Carr has ruled out running for the Labor leadership after the federal election in part because it would be hard to lead the parliamentary party from the Senate.
Senator Carr represented Australia as the country's foreign minister for the last time on Saturday in St Petersburg when he laid a wreath at a World War II cemetery.
Asked afterwards if he could be the next Labor leader after Kevin Rudd the minister replied: "No."
"I would rule it out," Senator Carr told reporters at the Piskaryovskoye cemetery where almost 500,000 people who died during the siege of Leningrad are buried in mass graves.
"It would be uncommonly hard to lead the opposition from the Senate.
"And I don't think the Australian people would want the convention about leadership from the House of Representatives to be breached - apart from any other reason."
Senator Carr insisted he would serve out his full term in the upper house.
"My desire to be regarded as the lion of the Senate is unchanged."
A number of Labor MPs have already admitted the federal coalition will win government on Saturday.
Senator Carr has been in Russia representing Australia at the G20 leaders' summit.