*Club domestic league appearances and goals, correct as of 23 December 2024 (UTC) ‡ National team caps and goals, correct as of 18:10, 30 November 2024 (UTC)
Harder is a product of FC Nordsjælland where he worked his way up through the youth ranks. After a strong 2022–23 season for the club's U-19 team, scoring 27 goals in 24 games, Harder made his official debut for FC Nordsjælland in the final Danish Superliga match of the 2022–23 season against Viborg FF, when the 18-year-old striker came on for the last three minutes of the match.[3][4]
He made four appearances in the first four games of the 2023–24 season, where he also scored his first goal for the club, before FC Nordsjælland announced on 5 September 2023, that they had signed a new three-year full-time contract with Harder, who would also be promoted permanently to the first team squad.[5] After a good start to the 2024-25 season, with two goals in Harder's second game of the season, the club confirmed on 22 August 2024 that they had extended Harder's contract until June 2028.[6]
Sporting CP
On 2 September 2024, Harder joined Primeira Liga club Sporting CP on a five-year contract for a fee of €19 million and a reported €80 million release clause.[7][8] Prior to signing for Sporting, Harder had attracted interest from Premier League club Brighton & Hove Albion, despite Nordsjælland accepting a bid from them, but upon learning of Sporting's interest, he decided to join them instead.[9][10]