[4] As one of the best prospects in the academy,[5] Radonjić moved to Partizan where he spent several, but later declared himself as a fan of the greatest opponent, Red Star Belgrade.

[6] Next he spent several months with Gheorghe Hagi Academy in Romania, before he signed a five-year contract with Roma in 2014, being loaned to Empoli for a season.

[15] Radonjić made his debut for Red Star Belgrade in the first leg of the third qualifying round for 2017–18 UEFA Europa League, replacing Ricardo Cavalcante Mendes in the 61st minute of the match against Sparta Prague, played on 27 July 2017.

[20] Returning to the field, Radonjić scored his first domestic league goal for Red Star Belgrade in the eternal derby match, played on 14 April 2018.

[23] On 25 July 2018, Radonjić scored a twice in the first leg of second qualifying round for the 2018–19 UEFA Champions League campaign,[24] after which he was also named as a player of the match in 3–0 victory over Sūduva.

[27] On 30 August 2018, Radonjić signed with French side Olympique de Marseille after helping qualify Red Star Belgrade for the group stage of the Champions League.

[30] Radonjić made his debut for the club in 4–0 Ligue 1 home victory over Guingamp on 16 September 2018, replacing Dimitri Payet in the 84th minute.

[34] On 3 September 2024 Radonjić signed a two-plus-one-year contract with Red Star Belgrade, marking his return to the club after six years.

[37] Radonjić was called into the Serbia U20 national squad in November 2016 by coach Nenad Lalatović, when made his debut for the team in a match against Montenegro.