N'Jie arrived at Lyon during the summer of 2011. He joined the under-19 squad and quickly progressed to the reserve squad along with Anthony Martial and Nabil Fekir, playing in the French 4th division. He played his first professional match during the 2012–13 season against Stade de Reims in a 3–0 win. N'Jie scored his first professional goal against Mladá Boleslav in the third qualifying round of the 2014–15 UEFA Europa League, helping his team to a 2–1 victory. On 13 August, he scored his first Ligue 1 goal in a 4–0 victory against Lorient. Earlier that day, he signed a three-year contract extension with Lyon through to 2019. Having been shortlisted for the 2014 CAF Most Promising Talent of the Year, N'Jie lost out to Porto and Algeria midfielder Yacine Brahimi. He finished his first full season at Lyon with eight goals and seven assists in 33 appearances, despite only starting half of his 30 league games, as he was the third piece of the Lyon attacking line, with Nabil Fekir and Alexandre Lacazette. N'Jie also finished the season with a 73% shot-on-target ratio, second to only to Paris Saint-Germain's Zlatan Ibrahimović, who ended the campaign on 74%.
Tottenham Hotspur
On 15 August 2015, English side Tottenham Hotspur announced that the club had reached an agreement for the signing of N'Jie from Lyon, subject to international clearance and a work permit. N'Jie agreed to a five-year contract with a reported transfer fee of €12 million. N'Jie made his Spurs debut on 17 September in a Europa League group stage match against Qarabağ, coming on as a substitute for Andros Townsend. On 10 December 2015, he tore his medial collateral ligament after a challenge by Jérémy Toulalan during a Europa League group stage match against Monaco. He had to undergo knee surgery for the MCL tear and was expected to out of action for at least 1–2 months, and possibly longer. Working with injured teammate Jan Vertonghen during his recovery, N'Jie eventually made his return on 8 May 2016 in a Premier League match against Southampton, in what would be his final appearance of the season. N'Jie made 8 appearances for Tottenham in the Premier League, his longest a 79-minute affair when he replaced the injured Nacer Chadli against Liverpool. In addition, N'Jie made 5 appearances, starting in 2 of them, in Tottenham's Europa League campaign, and did not score a goal in all competitions.
Marseille
On 31 August 2016, N'Jie returned to Ligue 1, joining Marseille on a season-long loan deal. Marseille had a €7 million option to buy him at the end of the loan, and Georges-Kévin Nkoudou headed to White Hart Lane on a permanent move in the opposite direction. On 11 September, he made his debut as a substitute for William Vainqueur in the 68th minute away to Nice, and he scored his first goal two weeks later to equalise in a 2–1 home win against Nantes. On 16 July 2017, N'Jie made his move to Marseille permanent, signing for an undisclosed fee. On 6 August, in the season opener against Dijon, he came on at half time for injured captain Dimitri Payet and scored two goals in a 3–0 win. On 17 September, he scored both the goals in the away win over Amiens. On 3 May 2018, he played in the Europa League semi-finals away to FC Red Bull Salzburg as Marseille played out a 2–1 away loss but a 3–2 aggregate win to secure a place in the 2018 UEFA Europa League Final.
Dynamo Moscow
On 25 July 2019, Njie signed a four-year contract with Russian Premier League club Dynamo Moscow. He scored his first goal for Dynamo on 27 October 2019, a late winner in a 1–0 victory over PFC CSKA Moscow.
N'Jie is a pacy forward who likes to play on the shoulder of the last defender, just off the front man. He can also play off the wing, and as dribbling is a key attribute of his game, he likes to take on players when given the chance. He frequently draws comparisons to Cameroon's all-time leading scorer and compatriot Samuel Eto'o, with this comparison being asserted by Lyon chairman Jean-Michel Aulas.
