Born in Niš,[3] Radonjić played in youth academy of the local club Radnički in his early years. Previously, he was a member of the local clubs Medijana and Železničar where he made his first football steps.[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.[7] At the beginning of 2016, Radonjić returned to Serbia, and joined Čukarički as a loaned player.[8] He scored a goal on his debut for Čukarički in the Serbian SuperLiga.[9] In the next fixture match, against Jagodina, he scored a goal from around 30 meters long distance of a goal, and later made assist for another goal.[10] Playing with Čukarički, Radonjić collected 31 appearances with 4 goals in all competitions until the end of 2016–17 season.[11]
Red Star Belgrade
On 21 July 2017, Radonjić moved to Red Star Belgrade.[12] He signed a five-year deal with his new club,[13] being formally loaned until summer 2019, when his contract with Roma will end.[14] He chose to wear the number 49 jersey at his new club.[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.[16] Radonjić scored his first goal for the club in the second leg of the play-off round for UEFA Europa League, in 2–1 victory against Krasnodar.[17] Radonjić played his first eternal derby on 27 August 2017, replacing Aleksandar Pešić in the 67th minute of the match.[18] Radonjić scored his second goal for Red Star in 1–1 draw to BATE Borisov on 14 September 2017.[19] Radonjić suffered a metatarsal bone fracture during the match against Rad on 18 November 2017. He became the third player in squad who injured in the same way since the beginning of the 2017–18 campaign, after Branko Jovičić and Vanja Vučićević.[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.[21] Later, Radonjić scored four goals in five played matches until the end of season,[11] including the last fixture match against Voždovac, when he won the first trophy in the professional career.[22] In May 2018, Radonjić was elected in the best 11 players for the 2017–18 Serbian SuperLiga season, by clubs captains' and managers' choice.[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.[25] Scoring in extra time of the match against Spartak Trnava on 14 August 2018, Radonjić secured the group stage of the 2018–19 UEFA Europa League campaign and play-off qualifying round for the Champions League, against Red Bull Salzburg.[26] On 29 August 2018, Red Star purchased the deal from Roma, keeping Radonjić until June 2021.[27]
Marseille
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.[28] He was assigned the number 7 jersey in his new club.[29] The transfer fee was reported as €12 million plus 2 million in bonuses.[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.[31]
Loan to Hertha BSC
On 1 February 2021, Radonjić joined German side Hertha BSC on loan for the remainder of the 2020–21 season.[32] While at Hertha BSC, Radonjić appeared in 12 games overall, scoring his first goal and getting his first assist in the same game against Freiburg. He played his last game for Hertha against TSG Hoffenheim before returning to France.
Loan to Benfica
He joined Benfica for the 2021-22 season on loan, he appeared in overall 11 games scoring one goal before returning back to France and being loaned out again, this time to Turin based club, Torino in Italy.
Torino
On 7 July 2022, Radonjić joined Serie A club Torino on loan from Marseille for the 2022–23 season. The deal included an option to make the move permanent for Torino, which was exercised at the end of the season.[33]
Loan to Mallorca
On 31 January 2024, Radonjić was loaned by Mallorca in Spain.[34]
Red Star Belgrade
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.[35]
In November 2022, he was selected in Serbia's squad for the 2022 FIFA World Cup held in Qatar.[45] He played in all three group stage matches, against Brazil, losing 2–0[46]Cameroon, drawing 3–3[47] and Switzerland losing 3–2.[48] Serbia finished fourth in the group.[49]