He signed for Premier League side West Bromwich Albion in 2011 for a fee of £6 million, and joined Hull City in January 2014, then Southampton in August 2014.

Long made his senior debut for the Republic of Ireland in 2007, earning 88 international caps and scoring 17 goals over a 14-year career with the national team.

[4] He was a talented hurler and appeared in two All-Ireland Minor Hurling Championship (under-18) semi-finals with Tipperary at Croke Park,[5] and was regarded as a pacey and promising forward.

[6] Long was also playing Gaelic football at this time, and started his career in the game with Two-Mile Borris club St Kevin's FC in 1994, joining St. Michael's in Tipperary Town in 2002.

[9] In Reading's Championship-winning 2005–06 campaign, Long scored three goals in ten substitute appearances,[10] making his first league start on 17 April 2006 in the 3–1 home victory against Stoke City.

[17] Long then scored a glancing header in the 100th minute in front of the Anfield Kop[18] from a cross supplied by Brynjar Gunnarsson, which sent Reading into the Fourth round of the FA Cup to play at home against Burnley.

[22] His goalscoring continued, as on 9 February 2010, he scored a brace in a 2–1 win at home to Plymouth Argyle, giving Reading their third consecutive league victory and Long's fourth goal in three games.

However, a hat-trick from Norwegian striker John Carew and a strike from Ashley Young in the second-half saw Long's brace go to waste as Aston Villa booked themselves a place in the semi-finals.

He marked his debut by scoring an equalising goal that went past Manchester United goalkeeper David de Gea, albeit in a losing effort, 2–1.

[40] Long suffered a chipped bone in his knee after a match against Aston Villa after a robust challenge by Alan Hutton, ruling him out for approximately six weeks.

On 19 November, weeks before he was predicted injury-free, he played 90 minutes against Bolton Wanderers, a game which Albion won 2–1, with Long scoring what proved to be the winner with a header against a much more physical opponent in David Wheater.

On 3 December, Long scored a goal off a deflected shot in the last minutes of a match against Queens Park Rangers earning Albion a draw by leveling the game at 1–1.

Clarke stated that Long was needed, as he did not have enough attacking options, despite signing Stéphane Sessègnon and Victor Anichebe just minutes earlier both for £6 million fees from Sunderland and Everton respectively.

[48] Long missed out on Hull's historic run to the FA Cup Final as he was cup-tied, having played in West Brom's third-round tie against Crystal Palace.

[50][51] They were his last official matches for Hull, as on 14 August 2014, Long signed a four-year contract with Southampton for an undisclosed fee, believed to be in the region of £12 million.

[52][53] Three days later, he made his first appearance for the club, replacing fellow debutant Dušan Tadić for the final 16 minutes of a 2–1 defeat at Liverpool in Southampton's opening game of the league season.

[55] He scored his first league goals for the club with a brace in a 2–0 win over Leicester City, having come on as a substitute for Sadio Mané with 22 minutes remaining.

[56] On 16 May 2015, Long assisted teammate Sadio Mané twice inside three minutes as the latter scored the fastest ever hat-trick in Premier League history during the first half of a 6–1 demolition of Aston Villa.

[57] In his first appearance the following season, Long scored Southampton's final goal in a 3–0 victory over Dutch opponents Vitesse Arnhem at St Mary's Stadium in the first leg of the Europa League third qualifying round.

[61] He ended a barren run of 23 games without a goal for Southampton on 31 December 2016, when he headed in against West Bromwich Albion at St. Mary's to give the home side a 1–0 lead.

[71] Due to injuries to his Reading teammate Kevin Doyle and Sunderland's Stephen Elliott,[72] he earned his first senior cap for the Republic of Ireland in their 2–1 win away to San Marino on 7 February 2007.

[73] When Long earned his second cap as a substitute against Slovakia on 28 March 2007 he became the first person to play both hurling and international football at Croke Park, having been part of the Tipperary team for the All-Ireland Minor semi-finals in 2003 and 2004.

[84][85] On 8 October 2015, Long again came off the bench to score the winning goal against reigning world champions Germany in another 2016 Euro qualifier in the Aviva Stadium.