Leeser holds the degrees of Bachelor of Arts (Hons.) and Bachelor of Laws from the University of New South Wales. He sat on Woollahra Council from 1995 to 1999. At the time, he was the youngest local councillor ever elected in Australia. In 1999 he served as a member of Prime Minister John Howard's "No" campaign during the republic referendum. In 2000, he was an associate to Justice Ian Callinan of the High Court of Australia.