Norwich City finally got their man when Gary Hooper signed for them on 26th July 2013, for an undisclosed fee rumoured to be £5.5million. He signed a three year contract. Norwich had first bid for him during the January 2013 transfer window.

Hooper joined the Tottenham Hotspur youth team at the age of seven. When he was 14 he played 20 minutes of a trial game and was then released by the club. After this he had trials with Northampton Town and Luton Town. These proved unsuccessful and he started playing non-league football with Maldon Town before being signed in the 2003/4 season by Conference side Grays Athletic.

He helped them win the Conference South title in 2004/5 scoring 12 goals. He started for Grays in the 2004–05 FA Trophy Final against Hucknall Town, but was substituted towards the end of extra-time. The match went to penalties and Grays won the shoot-out 6–5. The following season in the Conference, he scored eight times in 40 league appearances but was released at the end of the season.

In July 2006, after his release by Grays, Hooper went on two trials. Firstly to League Two side Barnet, then to Championship club Southend United, where he was given a one-year contract by manager Steve Tilson the following month. He made 18 appearances in the Championship with Southend but on 15th March, Hooper joined League One side Leyton Orient on loan for the rest of the season.

Hooper made 18 appearances in League One for Southend during the first half of the 2007–08 season, scoring twice. On 28th January 2008, Hooper signed a new 18-month contract to extend his stay with the club. He then moved on loan to League Two club Hereford United.

At the start of the 2008–09 season. Hooper, along with three other strikers, was listed for transfer as Tilson looked to re-build his attack. 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. Cheltenham Town had a bid accepted but Hooper eventually decided to move to Scunthorpe United. The fee was £125,000, rising to £175,000. He had scored four goals in 44 appearances for Southend.

He scored 30 goals in all competitions throughout the 2008–09 season and was Scunthorpe's Player of the Season. QPR had a £1million bid rejected whilst Coventry were also interested. He scored 20 goals in 39 appearances in all competitions in the 2009–10 season, including 19 in 35 in the league, where he finished as third-top goal scorer

On 26th July 2010, Scottish Premier League club Celtic signed Hooper for £2.4 million. He had made 95 appearances for Scunthorpe, scoring 50 goals. On 4th August 2010, Hooper scored on his debut for the club, against Portuguese Primeira Liga club Braga in the Champions League third qualifying round. He went on to make 138 appearances for Celtic, scoring 82 goals and finished leading scorer in the Scottish Premier League in 2011/12. He won two Scottish Premier League titles and the Scottish Cup twice.

He made his first appearance for Norwich in a 1-1 friendly draw at Brighton on 30th July 2013 before scoring a brace against Braga in a friendly on 2nd August 2013. Injured in a pre-season friendly against Panathinaikos, he did make his full City Debut until he came on as a substitute in the 1-0 home defeat to Aston Villa on 21st September 2013. Hooper got his first Norwich start on Tuesday 24th September away to Watford in the Capital One Cup and scored twice in a 3-2 win for Norwich.

He made 33 appearances, scoring eight goals in the 2013/14 season in which Norwich were relegated from the Premier League. At the end of the season, it was reported that he wanted to leave Norwich with QPR quickly linked with him. Transfer speculation at the end of August 2014 saw Hooper linked with QPR, West Ham and Crystal Palace even though he had not played in the Championship for Norwich due to injury.

In October 2014, Hooper was linked with a loan move to Bolton now managed by his former Celtic boss Neil Lennon.

Hooper scored his first hat-trick for Norwich in the 4-0 home win against Blackpool on 7th February 2015. He ended the season with 12 goals in 34 appearances as City won promotion back to the Premier League via the Championship play-offs.

He was linked throughout August 2015 with moves to Sheffield Wednesday and Fulham, reportedly having a medical at Fulham on transfer deadline day (1st September) but the move was not completed as Norwich hadn't secured an alternative striker. On 27th October 2015, he was loaned to Sheffield Wednesday until January 2016 as he was fifth choice striker in Alex Neil's plans. He scored six goals in 12 appearances on loan. Soon after his return to Carrow Road, he joined Wednesday on 22nd January on a three and a half year deal for an undisclosed fee.

After a missing a year out through injury, Hooper returned to playing action in March 2019 but was released two months later.

On 8th October 2019, reports from Iranian and Middle Eastern football writer Sina Saemian suggested that a proposed move to Bristol City had collapsed and that Hooper was in Turkey ahead of talks with Esteghlal of Tehran who play in the Persian Gulf Pro League, but have not won the title since 2013. However he then signed for Wellington Phoenix on 17th Octobe r2019. The New Zealand side compete in Australia's A-League. He is their marquee signing. Coach Ufuk Talay said "The wait has been worthwhile. With all the players we've gone through, we've gone through all their attributes and also their personalities to see how they would fit into the team environment, and Gary fits that mould. I'm very excited to have Gary here and look forward to getting him on the field. He fits into the way we want to play. We play with two strikers up front and Gary is very prolific in front of goal. If you look at his CV he's played over 400 games and scored close to 200 goals, and that's what we need in this team; someone who is going to score goals up front and also give us leadership. To have a player of his quality here is exciting not just for Wellington Phoenix but for the A-League, and I'm very happy that he's here"

After scoring eight goals in 21 appearances for the Phoenix in the 2019/20 season, he left them in September 2020 and was linked with a move to the Indian Premier League with the Kerala Blasters named as offering a one year contract. Their rivals Bengaluru FC and Chennaiyin FC also displayed interest in Hooper, according to reports in India. He completed a move to Kerala on 5th October 2020. “Gary has a natural killer instinct on the field and can score some unbelievable goals,” said Karolis Skinkys, sporting director of the Kerala Blasters. “I’m positive that our fans will soon come to love Gary for his high-level goalscoring quality. I’m very happy to have a player of such calibre join the team and look forward to working with him for our upcoming season.” Hooper added “I am really looking forward to the next chapter in my career with Kerala Blasters. I hope my experience can help the team and I can score important goals to help us challenge for the ISL title. Can’t wait to meet my teammates and start training for the new season.”

On 18th June 2021 he returned to the Phoenix on a two year deal as Kerala released all their overseas players on 11th June 2021. Hooper scored only five goals and provided four assists during his time in India.

His contract with Wellington was ended on 25th March 2022.

On 2nd September 2022 he signed for Cypriot side Omonia Nicosia. He played 13 games for Omonia, scoring twice.

On 10th February 2023 he signed for UAE club Gulf United who had just been promoted to their second tier. They are managed by former Newcastle defender Steven Taylor.

On 3rd October 2023 National League side Barnet announced that they had signed Hooper.

Earlier in his career, he was included in the England Under-21 squad in March 2011 but had to pull out due to injury. He was also linked with Scotland as his grandfather was born in the Scottish borders whilst the Welsh FA checked his eligibility in February 2012. He also expressed his interest in playing for Team GB at the London 2012 Olympics but wasn't selected.