Roukin was born in Southport and currently lives in northern New Jersey. He displayed an interest in drama from an early age. He completed secondary school at Merchant Taylors' School, Crosby where he was involved in many school productions. He goes back to the school to give acting workshops to pupils involved in drama and English. Roukin went on to train at the Bristol Old Vic Theatre School, graduating in 2003. Roukin finished filming Bright Star, directed by Jane Campion and based on the three-year romance between 19th century poet John Keats and Fanny Brawne. His last name is pronounced "ROH-kin."
Roukin starred in the 2008 film Happy-Go-Lucky as the love interest of the main character, Poppy (played by Sally Hawkins). Jonathan Romney's review of the film on the Independent website says of Poppy that "Realising one of her pupils is unhappy, she takes action that results in her meeting a simpatico social worker (Samuel Roukin), leading to possibly the single most convincing, no-nonsense, outright charming flirtation scene I've seen in cinema." The film, directed by Mike Leigh, won a host of nominations and awards worldwide. Roukin played a Snatcher in the two-part finale of the Harry Potter franchise, Harry Potter and the Deathly Hallows Part I & Part II. ITV's two-part drama pilot for the television series DCI Banks featured Samuel playing the lead villain. The two-parter was watched by over 5.5 million viewers. After Roukin's success in DCI Banks he was chosen to play the lead detective in the ITV1 Drama Appropriate Adult, a controversial drama regarding the capture of serial killers Fred West and Rosemary West. Samuel starred alongside two-time Oscar-nominated actress Emily Watson, who played Janet Leach, and Dominic West, who played Fred West. He played Bagot in the critically acclaimed Richard II, part of the cultural Olympiad of Shakespeare, directed by Rupert Goold and produced by Sam Mendes for BBC2 and NBC. Roukin currently portrays British Captain John Graves Simcoe, the main villain of the 2014 AMC series Turn: Washington's Spies, a period drama about the American Revolutionary War.