Amstell was born in Gants Hill, Redbridge, east London in 1979, to David and Tina (née Leventhal) Amstell. He was brought up in a Jewish family, and he was the eldest of four children. He was educated at Beal High School, a state comprehensive school in Ilford. His parents' divorce in the early 1990s has been a constant theme throughout his stand-up career, and he says that their decision when he was born to circumcise him had caused him a sense of great emotional as well as physical loss.