Pavan Rathnayake established his early cricketing credentials through the school system at Mahanama College, Colombo. Beginning his structured cricket journey in Grade One, Rathnayake was initially trained as a wicket-keeper before transitioning into a middle-order batsman who also bowled leg-spin.

Rathnayake made his first-class debut for Sri Lanka Police Sports Club in April 2019, in Tier B of the Premier League Tournament at seventeen years old. Seeking stronger competition, he subsequently moved to Colombo Cricket Club (CCC), where his T20 debut arrived in March, 2021, followed by selection for the SLC Blues team in the 2021 SLC Invitational T20 League.

Sustained domestic productivity earned Rathnayake his maiden national call-up late in 2025. He received his ODI debut cap (Cap No. 219) on November 16, 2025, against Pakistan at Rawalpindi Cricket Stadium, where he contributed a resilient 32 runs under pressure during a middle-order collapse. Shortly thereafter, on November 25, 2025, he made his T20I debut against Zimbabwe, establishing his initial presence in Sri Lanka's white-ball squads.

Rathnayake’s definitive international arrival took place on January 27, 2026, during the third ODI against England at the R. Premadasa Stadium in Colombo. Batting at number four in a demanding run chase, he registered his maiden ODI century, scoring 121 runs off 115 balls.

Following his breakthrough ODI performance, Rathnayake demonstrated professional ambition in early 2026 by declining a contract with Islamabad United in the Pakistan Super League (PSL). He prioritized red-ball preparation and Sri Lanka A duties to pursue his goal of earning a Test cap. This decision yielded immediate results when strong showings for Sri Lanka A in South Africa.

Concurrent with his red-ball ambitions, Rathnayake expanded his role in short-format international cricket during the ICC Men's T20 World Cup in February 2026. He produced vital innings, including a 25-ball 44 against Zimbabwe in Group B and a high-pressure 58 off 37 balls against Pakistan in the Super Eights at Pallekele. Rathnayake maintained his strong form through the middle of 2026 for Colombo Cricket Club. And given his consistency, he was picked for a white-ball English tour in September 2026.