Nsubuga began playing chess at age 14.[1] He is coached by Elijah Emojong.[2]
In 2011, he won the Junior Championship and the Uganda National Championship, being the only Ugandan player to accomplish this feat.[3]
In February 2018, he participated in the St Louis Chess Open and won the adult category ahead of Michel Zialor, Sergey Prokopyev, and Timothy Kate.[4] He later represented Uganda at the 2018 Chess Olympiad.[5]
Nsubuga was able to play in the Chess World Cup 2023[6] after obtaining the additional funding he needed to fly to Azerbaijan.[7] He was the second Ugandan after Arthur Ssegwanyi to participate in a Chess World Cup.[8] He was aiming to be able to become an International Master by earning two more IM norms through participating in the event.[9] At the event, he was defeated by Jules Moussard in the first round.