Lawther was born in Petersfield, Hampshire.[2] The youngest of three, he has said that his aspiration to be an actor came from having to make up his own games to entertain himself as a child.[3] His parents both work in law,[3] while his older brother, Cameron Lawther, is a film producer, and his older sister Ellie Lawther works in public policy.[4] In 2010, the brothers worked together on The Fear.