[9] Hooper joined Isthmian League Premier Division club Grays Athletic in the 2003–04 season,[10] being named as used substitute in an Essex Senior Cup match against Braintree Town on 11 November 2003 whilst he was still 15 years old coming on for Edward Erekosima.

[21] Hereford had a bid accepted for Hooper after his successful loan spell, but could not afford to match the larger transfer fees offered by other teams.

[27] Orient manager Martin Ling said that he thought Hooper had done well during his loan spell with the club and that he would monitor the progress of the young striker.

Scunthorpe manager Nigel Adkins said that he thought Hooper was a "massive threat" to the opposition and that he was worried that other teams would try to sign him before the end of the transfer window.

[44] He scored a hat-trick against Bristol City on his return from a groin injury on 17 April 2010,[45] and added a further two goals at Doncaster Rovers a week later.

[54] Hooper tore his calf muscle in a friendly against Blackburn Rovers just four days later on 8 August, keeping him out of action for almost six weeks.

[62] After recovering from an injury that kept him out of action during the Christmas period, Hooper returned to the team against Hibernian on 15 January 2011 and scored the opening goal in a 3–0 win.

[80] English Premier League clubs Queens Park Rangers and Wolverhampton Wanderers expressed interest in signing Hooper on transfer deadline day of summer 2011, however Celtic rejected their enquiries about his availability.

[97] On 1 August 2012, Hooper started the season in scoring form, in Celtic's 2–1 victory against HJK Helsinki in the first leg of the Champions League Third Qualifying Round.

[102] Celtic clinched their second successive Scottish Premier League title on 21 April 2013 with a 4–1 win over Inverness Caledonian Thistle at Parkhead.

[104] On 12 June 2013, English Premier League club Hull City made an undisclosed bid, believed to be about £4.5m, for Hooper which Celtic rejected.

[105] As transfer speculation increased over the summer, Hooper played what proved to be his final match for Celtic on 23 July when he came on a second-half substitute in a Champions League qualifier against Cliftonville.

[108] Hooper made his competitive début for Norwich on 21 September 2013 in a Premier League 1–0 home loss to Aston Villa as a 63rd-minute substitute.

[109] In his first start for the club, Hooper scored a brace to secure a 3–2 victory over Watford in the third round of the League Cup on 24 September.

On 7 December, Hooper scored his fifth Norwich City goal and third Premier League goal against West Bromwich Albion at The Hawthorns, a first time angled shot across goalkeeper Boaz Myhill into the corner after a through ball from Leroy Fer, the match ended in a 0–2 Norwich City victory.

[114] Hooper finished his first season at Norwich as the club's top scorer with eight goals, but was unable to prevent his team's relegation from the Premier League to the Championship.

By September 2015 he had only played ten minutes in the opening league match against Crystal Palace, and an 89th-minute substitute appearance against Southampton.

[106] A loan move to Sheffield Wednesday fell through despite the Yorkshire club agreeing to pay Norwich £500,000 and match Hooper's £32,000 weekly wage.

[122] Hooper denied press reports that the move collapsed due to his demand for Sheffield Wednesday to provide him with a VIP box at their stadium for his family and friends.

[124] Hooper made his first appearance for Sheffield Wednesday on 31 October 2015, coming on as a late substitute in a 1–0 win at home against Nottingham Forest in the Championship.

[125] In his seventh appearance in all competitions for the club, Hooper scored his first goal for Sheffield Wednesday in a 2–1 defeat at away against MK Dons.

[134] On 12 September, it was announced that Hooper had signed a one-year deal with the Indian Super League club Kerala Blasters FC.

[144] On 3 October 2023, he returned to English football to sign for National League club Barnet, subject to international clearance.

[145] Hooper scored twice in 14 appearances in the first two months after signing, but did not play for the club again after December and was released at the end of the season.

[156] In February 2012, BBC Sport reported that the Football Association of Wales were investigating his eligibility, but Hooper was unaware of having any Welsh ancestry.

They were handed a bleak prognosis by Celtic's medical team, meaning Hooper couldn't make the squad through injury.

Claridge noted that Hooper needed to work harder to make himself available to his teammates for passes, especially long balls out from defence.

They scored over 40 goals between them in their first season together and were considered to be Celtic's best strike partnership, although on many occasions, especially for big matches, Georgios Samaras was often used alongside Hooper.

Stokes usually played a deeper role, coming short to get the ball and creating space through his dribbling skill and passing.

[165][166] During his time as manager at Rangers, Ally McCoist showed his players footage of a goal Hooper scored against them at Celtic Park.