Cox scored his first goal for the club in a 3–0 win away at Sheffield United on 16 August 2016. On 26 June 2018, Cox signed a new contract at Southend   On 16 January 2020, Western Sydney Wanderers signed Cox to play in the A-League, joining on a one-and-half-year deal. Cox is eligible to play for the Republic of Ireland through his Irish-born grandmother. He was first called up to the Republic of Ireland squad by Giovanni Trapattoni on 5 May 2011, as a replacement for Damien Duff. Cox made his international debut on 24 May 2011 in the 2011 Nations Cup game against Northern Ireland, when he scored the fifth goal in a 5–0 victory. He went on to win four caps in the next two weeks, and scored his second international goal in a 2–0 friendly defeat of Italy in Liège on 7 June 2011. On 11 October 2011, he played and received the "Man of the Match" award in the game against Armenia, helping secure his team a place in the play-offs for UEFA Euro 2012. He scored the equaliser in the 1–1 friendly against the Czech Republic at the Aviva Stadium on 29 February 2012. Cox was selected in Trapattoni's 23-man squad for the UEFA Euro 2012. Cox scored his 4th goal for Ireland in a 4–0 win over Georgia on 2 June 2013. On 6 September 2013, after coming as a second-half substitute in a World Cup qualification match against Sweden, it was supposed that he has suffered a dead leg and would battle for fitness. However, Cox's club, Forest, denied any such allegation. Republic of Ireland  Individual