Born and raised in London, Marsan came from modest means and was poised to become a printer until his fascination with theater pulled him to the stage. After attending the Mountview Academy to study acting and toiling away in small theater productions, he finally began to win parts on British television, with walk-on spots soon giving way to bigger roles. His key part as Brian Clapton on the post-WWII comedy "Get Well Soon" (BBC, 1997) elevated his profile considerably, leading to supporting roles in a 1998 TV-movie version of the Russian literary classic "Crime and Punishment" (NBC) and the English thriller "Gangster No. 1," starring Paul Bettany in a career-establishing role. Marsan went on to join the scrappy ensemble cast of Martin Scorsese's "Gangs of New York" and portray a man of the cloth in the moody drama "21 Grams," featuring Sean Penn and Naomi Watts. Completely fitting the bill as one of Mike Leigh's rough-around-the-edges characters, Marsan proved to be an excellent addition to the British writer/director's stable of actors when he was featured in "Vera Drake" (2004), starring Imelda Staunton as a compassionate woman defying convention in 1950s London. Although Marsan continued to appear on English TV, he focused primarily on film in subsequent years, with small parts in major cinematic undertakings, including the heady dystopian action film "V for Vendetta" (2005), Terrence Malick's highly anticipated period drama "The New World" (2005) and the blockbuster spy movie "Mission: Impossible III" (2006). In 2008, Marsan unofficially became the heir to Bob Hoskins' brand of fierce, bulldog-like acting, with notable turns in the down-and-out superhero tale "Hancock" and the biopic "Me and Orson Welles." However, even these roles were outshined by his seething performance as the bitter driving instructor Scott, who clashes with Hawkins' ever-cheerful Poppy in Leigh's widely lauded dramedy "Happy-Go-Lucky" (2008). Returning to British television for a featured part on the BBC miniseries "Little Dorrit" (2008), Marsan later played a gay kidnapper holding Gemma Arterton's character hostage in the tense thriller "The Disappearance of Alice Creed" (2009) and made his bearded face known to millions of movie goers as the cranky Inspector Lestrade in Guy Ritchie's hit reinterpretation of "Sherlock Holmes" (2009). Before appearing on 2011 holiday screens in both the "Holmes" sequel, "A Game of Shadows," and Steven Spielberg's World War I film "War Horse," Marsan gave another exceptional performance in Paddy Considine's "Tyrannosaur," where he portrayed a vicious abusive husband. After starring in the dramatic TV movie "The Best of Men" (BBC, 2012) and apparently tiring of weighty fare, he shifted to supporting roles in the fantasy features "Snow White and the Huntsman" (2012) and "Jack the Giant Slayer" (2013). And, in a collaboration that seemed all but inevitable, Marsan signed on to Edgar Wright's uber-British apocalypse comedy "The World's End" (2013), reuniting him onscreen with Considine while struggling for survival with the always-hapless Simon Pegg and Nick Frost.