Jackson joined Rushden & Diamonds in 2004 and was the club’s top scorer in the 2006–07 season, scoring 20 goals. The next season, he was top scorer for the Diamonds in the league, scoring 16 goals, despite leaving for Gillingham in January. He was joint eighth top scorer in the league that season. In 2005, he had trials with Manchester United and Manchester City. Jackson went on a one-month loan to Raunds Town in December 2005. When he left the Diamonds he had established himself as the club’s eighth highest goalscorer, scoring 43 goals in just over 100 games in all competitions.

Jackson qualified for Canadian citizenship by virtue of his years of residence there as a child, and currently has 45 caps for Canada, scoring six times. He also has seven caps for the Canadian men’s youth (under-20) team. His first game was a friendly against Brazil in May 2006, and he played in all three of Canada’s games at the 2007 U-20 World Cup, his last games at that level. On November 14, 2008, he received his first call up for the Canadian senior squad for a match against his country of birth, Jamaica.

In January 2008, Jackson signed with Gillingham, a club he had a trial with as a youth player, for a transfer fee of £150,000 on a three-and-a-half-year contract. He made his debut against Cheltenham Town on February 2, 2008.

On January 4, 2009, Jackson scored an equalizing goal for Gillingham in their 2–1 FA Cup Third Round defeat by Aston Villa. He scored both goals as Gillingham beat Rochdale in the 2008–09 play-off semi final, and the 90th-minute winner in the 1–0 win against Shrewsbury Town in the final, as Gillingham returned to League One one year after relegation.

Following his Premier League debut, Jackson began to struggle finding minutes in the team, he did not play a minute of football in the league until October 1 as a second half sub against Manchester United. Jackson made his first start in the Premier League on November 26 in a 2–1 victory over Queens Park Rangers, this was the first time a Canadian international had started in the Premier League since David Edgar on May 24, 2009 with Burnley. Jackson scored his first Premier League goal on December 20 against Wolverhampton Wanderers when he converted a Steve Morison cross one minute after being subbed on. Jackson came on as a second half sub against Fulham on December 31 and scored the game tying goal in second half injury time to earn a 1–1 home draw. In the fourth round of the FA Cup in late January Norwich was drawn against West Bromwich Albion, Jackson came off the bench in the 65th minute with the game being tied at 1–1 and scored the winning goal in the 85th to take the Canaries into the fifth round. After failing to make an appearance for almost a month Jackson returned to the starting line up in a 3–3 away draw on 5 May against Arsenal. The following week, Jackson was given the start again in the final game of the season against Aston Villa, the game ended in a 2–0 home victory with Jackson and Grant Holt as the scorers. Jackson finished the 2011–12 campaign for Norwich having made 22 appearances, starting in 10 of those. He scored three goals and registered two assists, with 34 shots on goal in his debut Premier League season. The club took up the option to extend Jackson’s contract for another year in June 2012, along with David Fox and Elliott Ward. On August 25, 2012 he scored his first goal of the new season in a 1–1 draw at home to Queens Park Rangers. At the end of the season, Jackson was released by Norwich, having struggled to find minutes during his second year in the top flight.

On May 30, 2009, Jackson made his debut for Canada against Cyprus, scoring the winning goal in the 53rd minute of a 1–0 victory. Jackson helped Canada reach the quarter-final stage of the 2009 CONCACAF Gold Cup in the US, playing in all four of Canada’s games in the tournament. On December 18, 2009, Jackson was named the Canadian Player of the Year.

Jackson signed for Norwich in July 2010, signing a two-year contract with the club, with the option for another year, in a deal which saw striker Cody McDonald move to Gillingham on loan. He was given the number 10 jersey upon his arrival at the club and made his debut in a 3–2 home loss to Watford on August 6, 2010. He scored his first goal for the club against Swansea City on August 21. Manager Paul Lambert often used Jackson as an impact substitute due to the form and partnership of Grant Holt and Chris Martin. Jackson was given a start against Bristol City, and scored a brace, with a goal in each half at Ashton Gate. Jackson started the next four games again, in favour of Martin. He scored his fourth goal of the season in the 1–0 win over Middlesbrough on October 23. After a few months of mostly coming in as a substitute again, on April 2, 2011, Jackson scored his first hat-trick for Norwich, coming on as a substitute and scoring three times in the last twenty minutes of the match against Scunthorpe United at Carrow Road. He went on to score the goal that clinched Norwich’s promotion to the Premier League, a late winner against Portsmouth.

National team coach Stephen Hart decided in the friendly versus Peru to experiment by using Jackson as a right winger. With a solid performance at BMO Field Hart continued to use Jackson out wide for future Canada match ups. On October 8, 2010, Jackson scored his second international goal with a chip in a friendly against Ukraine. On October 7, 2011, Jackson scored a hat-trick against Saint Lucia in a game that finished in a 7–0 away victory for Canada. Jackson became only the second ever Canadian to score a hat-trick in World Cup qualifying joining the former striker Alex Bunbury. In early December, Jackson was shortlisted for the 2011 Canadian Player of the Year along with Dwayne De Rosario and Josh Simpson, it was announced on December 14 that he had finished in second place losing out to De Rosario.

Jackson made his Premier League debut on August 21, 2011, as a second-half substitute for Chris Martin in the second game of the season against Stoke City, the game finished with a Kenwyne Jones stoppage time header which resulted in a 1–1 home draw for Norwich.

On June 1, 2011, it was announced by Umbro that Jackson had signed an endorsement deal following the new partnership between the English sportswear company and the Canadian Soccer Association, making Jackson one of the few Canadian players to have an endorsement deal. In 2012, Jackson revealed that “he plans to fulfil a long-held dream next year when he sets up his first ‘soccer’ school in Southern Ontario … “I want to help kids in Canada improve themselves, and get the opportunity to play in Europe and at the highest level through a soccer school.”

On July 10, 2013, Jackson signed for German Bundesliga side Eintracht Braunschweig on a two-year contract. Jackson was previously linked with a move to Championship side Bournemouth. After just nine appearances during the first half of the season, Jackson and Eintracht Braunschweig mutually agreed to terminate his contract on January 31, 2014.

On February 1, 2014, a day after his Eintracht Braunschweig contract was terminated, Jackson agreed to join Championship side Millwall on a deal until the end of the season. He made his debut against Brighton & Hove Albion on March 1, 2014. Jackson scored his first goal on March 25 in a 3–2 home defeat to Birmingham City.

On August 18, 2014, Jackson signed for League One team Coventry City on a one-year contract. On September 13 Jackson scored his first goal for the club and the game-winning goal in a 2–1 victory over Yeovil Town.

After leaving Coventry at the end of the 2014–15 season, Jackson went on trial at fellow League One side Barnsley. On September 3, 2015, he signed a short-term contract to keep him at the club until January 3, 2016.

Following a successful trial, Jackson signed a short-term deal with Blackburn Rovers on January 15, 2016 to last until the end of the 2015–16 season. He scored his first goal for Blackburn in a 2–1 defeat to Leeds United on March 12, 2016.

Jackson signed for Walsall on July 18, 2016, and scored twice on his debut for Walsall in a 3–1 win over AFC Wimbledon on August 6, 2016. In January 2018 he joined Grimsby Town on loan for the remainder of the 2017–18 season.

Jackson went on to a trial spell with Scottish Premiership club St Mirren in September 2018 and was signed on a short-term deal through January 2019. He left Saints when his contract expired in June 2019, having helped the club avoid relegation.

Jackson signed a short-term contract with Scottish Premiership club Kilmarnock in October 2019. Jackson left after the expiration of his contract in December 2019.

On January 20, 2020, Jackson signed a six-month deal for Stevenage. After only five appearances in all competitions Jackson was released by the club at the conclusion of the 2019–20 season, which saw the Hertfordshire club relegated to the National League.