On 24 June 2013, McCormack signed a two-year contract with Brentford, who had remained in League One after suffering defeat in the 2013 League One play-off Final. He began the 2013–14 season in his natural midfield position, before being moved to right back by manager Uwe Rösler in October, to replace out-of-form Shay Logan. McCormack scored his first Brentford goal in an FA Cup first round tie against local neighbours Staines Town on 9 November, opening the scoring with a penalty in a 5–0 victory. A near ever-present under Uwe Rösler and his successor Mark Warburton, McCormack celebrated promotion to the Championship after a 1–0 victory over former club Preston North End on 18 April 2014. He finished the 2013–14 season with 45 appearances and two goals. McCormack won the Brentford Supporters' Player of the Year award and was named as the right back in the League One Team of the Year.