On 1 July 2012 McCartney rejoined newly promoted West Ham signing a two-year contract after agreeing to make the loan move permanent. In November McCartney suffered a serious knee injury playing against Liverpool. He made his comeback on 30 March 2013 against West Bromwich Albion but lasted only 15 minutes before a recurrence of the same injury which was expected to keep him from playing for the remainder of the 2012–13 season. McCartney returned to the first team for a League Cup game against Cheltenham Town on 27 August 2013. His Premier League return however was not until 30 November 2013, in a 3–0 win against Fulham. McCartney was released by West Ham at the end of the 2013–14 season. McCartney had played 82 games in all competitions in his second spell with the club, scoring a single goal.