On 28 June 2012, Fournier was selected with the 20th overall pick by the Denver Nuggets in the 2012 NBA draft. On 11 July 2012, he signed his rookie scale contract with the Nuggets. He then joined the Nuggets for the 2012 NBA Summer League. Over the Nuggets' first 73 games of the 2012–13 season, Fournier had appeared in just 29 of them and while registering 10 points or more just once. He appeared in nine straight games to finish the regular season, including starting the final three. During this late-season stretch, he averaged 12.3 points and scored 17 points or more four games, including a season-best 24 points on 14 April 2013. In July 2013, Fournier re-joined the Nuggets for the 2013 NBA Summer League. On 30 October 2013, the Nuggets exercised their third-year team option on Fournier's rookie scale contract, extending the contract through the 2014–15 season. On 23 February 2014, Fournier scored a then career-high 27 points against the Sacramento Kings.
Orlando Magic (2014–present)
On 26 June 2014, Fournier was traded, along with the draft rights to Devyn Marble, to the Orlando Magic in exchange for Arron Afflalo. On 26 October 2013, the Magic exercised their fourth-year team option on Fournier's rookie scale contract, extending the contract through the 2015–16 season. On 12 November 2014, Fournier scored a then career-high 28 points on 8-of-14 shooting in a 97–95 win over the New York Knicks. On 3 November 2015, Fournier set a new career high with 30 points in a 103–94 win over the New Orleans Pelicans. On 15 March 2016, Fournier matched his career high with a 30-point effort against the Denver Nuggets. In 2015–16, Fournier had a career year in which he averaged personal highs in scoring, rebounding, assists, steals and minutes. He led the team in scoring 19 times, had 24 20-point games and two 30-point games. On 7 July 2016, Fournier re-signed with the Magic on a five-year, $85 million contract. On 3 November 2016, he scored a season-high 29 points against the Sacramento Kings. On 16 January 2018, Fournier scored a career-high 28 points plus 4 in a 108–102 win over the Minnesota Timberwolves. On 7 March 2018 against the Los Angeles Lakers, Fournier sprained his left medial collateral ligament. He was subsequently ruled out for "a significant stretch of time". On 1 December 2019 Fournier tied his career high of 32 points in a game in a 100-96 win over Golden State. His first 32 point career game included overtime, this was his first time with 32 points in regulation.
