Mendis started bowling with both arms at the age of 13 while playing cricket for Richmond College, Galle.

He made his List A debut alongside Charith Asalanka on 30 November 2015 in the AIA Premier Limited Over Tournament.

[14] He made his first-class debut for Tamil Union Cricket and Athletic Club in the 2018–19 Premier League Tournament on 30 November 2018.

[19] In November 2021, he was selected to play for the Kandy Warriors following the players' draft for the 2021 Lanka Premier League.

[21] In August 2018, Sri Lanka Cricket named him in a preliminary squad of 31 players for the 2018 Asia Cup.

[25] In February 2019, he was named in Sri Lanka's One Day International (ODI) squad for their series against South Africa.

[27] In November 2019, he was named as the vice-captain of Sri Lanka's squad for the 2019 ACC Emerging Teams Asia Cup in Bangladesh.

[28] Later the same month, he was named as the vice-captain of Sri Lanka's squad for the men's cricket tournament at the 2019 South Asian Games.

[29] The Sri Lanka team won the silver medal, after they lost to Bangladesh by seven wickets in the final.

[30] In September 2021, Mendis was named in Sri Lanka's squad for the 2021 ICC Men's T20 World Cup.

[36] In the match, he scored his maiden Test fifty and made a match-winning partnership of 133-runs with centurion Dinesh Chandimal.

Sri Lanka piled 531 runs on the board, which is the highest total in a Test innings without a single century.

Mendis was again adjudged as the player of the series along with England batter Joe Root for scoring 267 runs with 53.40 average and strike rate of 63.