[4] Born in Dublin, Henderson began his youth career with Belvedere before joining Aston Villa in 2005 at the age of 17.

[9] He joined Weymouth of the Conference Premier on a one-month loan on 29 February 2008 and spent the rest of the 2007–08 season with the club, making 16 appearances.

[17] On 3 January 2011, Henderson re-joined Yeovil on loan for the remainder of the season and subsequently kept a clean sheet on his return against Brentford.

[17][18] On 8 July 2011, Henderson joined Portsmouth on a three-year contract, citing his reasons for leaving Bristol City as frustration at his lack of first-team opportunities.

[22] On 16 March 2012, Henderson joined Championship rivals West Ham United on an emergency loan from Portsmouth until the end of the season.

[23] He was unused substitute for the 2012 Championship play-off final, a result that ensured West Ham made an immediate return to the Premier League.

[25] He made his first-team debut for West Ham on 28 August 2012 against Crewe Alexandra in the League Cup.

[5] Henderson was called up to the senior national team for a February 2012 friendly match against the Czech Republic, for which he was an unused substitute.