*Club domestic league appearances and goals, correct as of 12:57, 18 December 2024 (UTC) ‡ National team caps and goals, correct as of 7 September 2024
Arnór was described as a key player for Norrköping in the 2018 Allsvenskan season, where he played as an attacking midfielder.[4][5]
CSKA Moscow
On 31 August 2018, Arnór signed a five-year contract with the Russian Premier League club CSKA Moscow.[6] The transfer fee was reportedly set at around 40 million Swedish kronor (approximately €4 million), a club record fee received by Norrköping.[7] He made his debut for CSKA on 19 September 2018 in a game against Viktoria Plzeň, and became the youngest Icelandic player ever to appear in a UEFA Champions League game.[8]
On 30 July 2021, he joined Italian Serie A club Venezia on loan for the 2021–22 season. Before going on loan, he extended his contract with CSKA until 2024.[12]
Return to Norrköping
On 3 July 2022, Arnór suspended his contract with CSKA Moscow for the 2022–23 season, having taken advantage of the FIFA ruling relating to the Russian invasion of Ukraine.[13] On 14 July 2022, he returned to Norrköping until June 2023 under these regulations.[14]
Blackburn Rovers
On 21 June 2023, Arnór again exercised his right to move clubs and joined Blackburn Rovers for the 2023–24 season.[15] On 26 December 2023, the transfer was made permanent, and Arnór signed a contract with Blackburn until June 2025.[16]