[1] He made his international debut for the Sri Lanka cricket team in June 2022 to a series against Australia.
[3] Wellalage made his List A debut on 14 December 2019, for Lankan Cricket Club in the 2019–20 Invitation Limited Over Tournament.
In January 2022, he was named as the captain of Sri Lanka's team for the 2022 ICC Under-19 Cricket World Cup in the West Indies.
[6] In Sri Lanka's opening fixture of the tournament, he took a five-wicket haul,[7] and was named the player of the match.
[19] In July 2022, he was again named in Sri Lanka's Test squad, this time for their home series against Pakistan.