Hammill is a product of the Liverpool academy, but failed to make a league appearance for the club at senior level, before leaving to join Championship side Barnsley in 2009.
[citation needed] In January 2007, he got his first taste of senior football when he was loaned to Scottish side Dunfermline Athletic until the end of the season.
[12][13] Having regained his first team place, Hammill then provided two assists for the club, as Southampton beat Hull City 4– 0 on 8 December 2007.
Returning to Anfield, he signed a new five-year contract with Liverpool in July 2008, before being sent out on loan for a sixth time; joining Blackpool in a six-month deal.
[16] In the next game against Norwich City on 16 August 2008, Hammill won a penalty in the 55th minute, which Ben Burgess successfully converted, in a 1–1 draw.
[17] He scored his first goal in English football for the Seasiders on 16 November in the West Lancashire derby 3–1 home defeat to Preston.
[22] Hammill made his Barnsley debut in his first spell on 17 February 2009, where he came on as a substitute for Andranik Teymourian in the 80th minute, in a 1–0 win over Sheffield Wednesday.
[25] Following his loan spell at Oakwell in Spring 2009, Barnsley launched a bid which was turned down as Liverpool wanted to see what Hammill could offer during pre-season.
[30] Hammill's first game after signing for the club on a permanent basis came on 11 August 2009 in a League Cup first round tie, with a 1–0 win at Lincoln City.
[49] Hammill was previously linked with a move to Premier League's rival and his former club, Blackpool, before joining Wolverhampton Wanderers.
[51] He made ten appearances in total for the club during the remainder of the season, but found himself on the sidelines towards the end of the campaign as manager Mick McCarthy recalled the more experienced Stephen Hunt.
In total he made 27 appearances for Wolves, scoring once, before his time at Molineux ended as Kenny Jackett arrived as manager.
[59] Shortly before the end of the transfer window on 31 August 2012, he joined fellow Championship side Huddersfield Town in a loan deal to last until 13 January 2013.
[62] His only other goal for the Terriers happened to be his final kick of his loan spell with a last minute equaliser against Birmingham City in January 2013.
However, Hammill felt out of favour with Huddersfield Town manager Chris Powell, and subsequently was dropped from the team's match-day squad, as well as, his own injury concern.
[79][80] After four months absent, Hammill made his first appearance when he come on as a substitute in the 84th minute, in a 2–1 win over Bolton Wanderers on 28 December 2014.
[86][87] Though he made five appearances at the start of the 2015–16 season, which saw his shirt number changed from twelve to twenty-five,[88] it was announced on 1 September 2015, he was released by Football League Championship side Huddersfield Town by mutual consent.
[94] Hammill then scored his second goal against Wigan Athletic and Barnsley won 4–2 on penalties after the game was played for 120 minutes in the Semi-Final of Football League Trophy.
[96] Shortly signing a contract with Barnsley, Hammill scored his first league goal since 2010, in a 3–2 win over Colchester United on 12 December 2015.
[104] Hammill went on to play a vital role in the League One play-offs promotion to the Championship when he scored two times in three appearances against Walsall in the second leg[105] and the final against Millwall.
Along with then Liverpool teammates Craig Lindfield and Paul Anderson, Hammill was called up for the England under-19 team in 2006, and scored his first Under-19 international goal in the win against Switzerland in November 2006.
[121] On 27 March 2011, Hammill was called up to the England U21 squad for the first time, as Stuart Pearce had a number of injuries and made the decision to rest some key players.
On 28 March 2011, it was confirmed that Hammill is eligible to play for the Republic of Ireland national side through his late grandfather.
[127] In the early hours of 7 October 2012, Hammill was involved in an altercation outside a Liverpool nightclub while celebrating a friend's birthday and was arrested for assaulting two female paramedics.