In 2009, Merrells had a lead role in the 2009 film, Invisible Eyes. In 2010, he portrayed Ben Talbot, brother of Lawrence Talbot in remake of The Wolfman. In 2013, he portrayed the Roman commander Marcus Licinius Crassus in the Starz series Spartacus: War of the Damned. He had to undergo a strict diet and four-week fitness boot camp in preparation for the role, losing 21 lbs. Also that year, he portrayed character Mark Vega in the British horror film Judas Ghost. He also plays The Founder in the 2013 American remake of The Tomorrow People.