After appearing in two episodes of the television series Shameless, Warren played the evil Andy Holt in Channel 4's teen soap opera Hollyoaks. Despite being 27 years old at the time, it was said his youthful good looks helped him win the role of the student. It is arguably his most famous role to date. Brown was nominated for a number of awards for his performance in the show including Best Villain, Most Spectacular Scene and Best Exit at the 2006 British Soap Awards. Brown's character Holt met his demise in February 2006.

Brown won a role in the short-lived ITV show Jane Hall in the summer of 2006. This was followed in March 2007 by his role as Tommo in ITV's Mobile. Also in 2007 he starred as Chris in one episode of Casualty. In September 2007 he starred in the second series of BBC Three's Grownups, playing barman, Alex Salade and has played the part since. In the 2009 Comic Relief Special of Two Pints of Lager and a Packet of Crisps, which was a crossover between Grownups, Two Pints and Coming of Age, he played Alex again.

In 2008 Brown performed the voiceover for the film trailer on the soon to be released Gomez: A True Story based on the life of boxer Michael Gomez and starring Emmerdale's Kelvin Fletcher. In October 2008, Brown played the role of Marky in E4's zombie drama Dead Set. In November 2008 he appeared in Casualty, but not playing the same character as he did in 2007. In 2009 Brown appeared in the three part BBC TV Iraq war drama Occupation, alongside James Nesbitt and Stephen Graham Recently he has appeared in two episodes of The Bill playing Jake Clegg, who is a part of the operation of trafficking young girls illegally. These episodes were titled "The Forgotten Child".

As of May 2010, he appears as the regular character of DS Justin Ripley in the BBC TV drama Luther.

Brown appears in the Deadmau5 music video for the song "I Remember".

As of September 2010, Brown will appear in the BBC drama "Single Father", as Matt.