Sam, born in Hammersmith, London, is the son of actor James Hazeldine and Rebecca Moore.
After moving between London and Manchester, his father's hometown, the family settled in Tottenham, North London where Sam attended Lancasterian Junior School until the age of 8. When Sam's father moved to Stratford-upon-Avon for the Royal Shakespeare Company's 1980 and 1981 seasons, Sam was taken out of school in London to accompany him. He spent much of his time watching his father in rehearsal rooms there before returning to Tottenham.
With tensions rising in North London and following repeated burglaries, the family left their Broadwater Road home and moved to Banbury, Oxfordshire, where Sam attended Banbury School until the age of 16.
Sam attended the Royal Academy of Dramatic Art (RADA) along with Andrew Lincoln, Shaun Parkes, Jonathan Slinger, Stephen Mangan, Sarah Preston and Dawn McDaniel amongst others, before leaving in 1993 to pursue a career in music.