Spajić made his professional debut for Red Star Belgrade on 27 October 2010 in a Serbian Cup match against Borac Čačak.

He was subsequently loaned to Red Star's farm team Sopot in the Serbian third tier, where he played the 2011–12 season.

[2] On 29 May 2013, Red Star Belgrade and Toulouse FC agreed on Spajić's transfer to the French side for €1.5 million.

[12] On 18 February 2025, Chinese Super League club Beijing Guoan announced that it has completed the signing of Spajić.

Spajić was selected in Serbia's squad for the UEFA Euro 2024, but didn't make any appearances in the tournament.