Mazer attended The Haberdashers' Aske's Boys' School, where he met Baron Cohen. He went on to read Law at Peterhouse, Cambridge University, and graduated in 1994. He was an active member of Cambridge Footlights while at university and was vice President from 1993 to 1994.
In 2007, he was nominated for an Academy Award for Best Adapted Screenplay for co-writing the film Borat: Cultural Learnings of America for Make Benefit Glorious Nation of Kazakhstan. He shared his nomination with Sacha Baron Cohen, Ant Hines, Peter Baynham, and Todd Phillips. They ended up losing to The Departed. He is currently co-writing Lost for Words with Jamie Curtis.
In 2013 he made his feature film directing debut with the British comedy I Give It a Year. He followed it with the 2016 American comedy Dirty Grandpa.
