Hockey, who belongs to the ruling Liberal Party, is a long-time member of Arm and supported the failed republican bid in the 1999 referendum.
The announcement comes at an awkward time for the Treasurer, who has been focused on taxation reform and dousing fears of market volatility.
He drew a mixed reaction from political colleagues yesterday, with some suggesting he should keep his focus on the economy.
Dean Smith, a fellow Liberal and a supporter of the monarchy, said the campaign was "most definitely a distraction", according to ABC.
"Mr Hockey has long advocated his views on this issue," a spokeswoman told the Daily Telegraph. "Those views haven't changed."
Tim Mayfield, Arm's national director, said the movement had been set back by the referendum loss in 1999 but denied it had been dormant since then. "The movement's done a lot but it's been an uphill battle because people haven't been interested. There just wasn't the political will," Mayfield said.
Fitzsimons said: "Hopefully the stars will align and we will get an Australian prime minister and an Australian opposition leader who are both republicans."