[1] He made his international debut for the Sri Lanka cricket team in March 2021 and is currently the permanent opening batsman.

[2] On 9 February 2024, Nissanka scored an ODI double hundred, becoming the first Sri Lankan to achieve the feat.

[5] He started his cricket career during his time at Kalutara Vidyalaya and then move to Isipathana College, Colombo.

[6] When in the School Cricket Championship he scored an unbeaten double century (205) off 190 balls against President's College, Rajagiriya at Colts ground, Colombo.

[14] In November 2021, he was selected to play for the Colombo Stars following the players' draft for the 2021 Lanka Premier League.

[15] In July 2022, he was signed by the Kandy Falcons to play in the 2022 Lanka Premier League tournament.

[16] On 17, December 2023 at Major Clubs Limited over tournament 2022/2023, against SSC Pathum scored his 5th List A century.

[19] He finished the tournament as the leading run-scorer for Nondescripts Cricket Club, with 1,088 runs in seven matches.

[20] In November 2019, he was named in Sri Lanka's squad for the 2019 ACC Emerging Teams Asia Cup in Bangladesh.

[21] Later the same month, he was named in Sri Lanka's squad for the men's cricket tournament at the 2019 South Asian Games.

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

[23] In February 2021, Nissanka was named in Sri Lanka's limited overs squad for their series against the West Indies.

[25] Three days later, Nissanka was named in Sri Lanka's Test squad, also for their series against the West Indies.

[26] He made his One Day International (ODI) debut for Sri Lanka on 10 March 2021, against the West Indies.

[30] On 1 October 2021, he was added to Sri Lanka's squad for the 2021 ICC Men's T20 World Cup.

[33][34] Even though Sri Lanka lost the T20I series 4-1 against Australia in February 2022, Nissaka broke the record for runs scored by a Sri Lankan batsman in a T20I match series against Australia, scoring 184 runs in the 5 matches.

[38] During the 2022 Asia Cup, Nissanka played as the opener with Kusal Mendis and they made match-winning partnerships in the games against Bangladesh, Afghanistan and India.

[49] On 7 July 2023, qualifier match against West Indies, Pathum Nissanka scored his second consecutive and third ODI century.

[50] Nissanka was the second-highest run-scorer in the World Cup qualifier, scoring 417 runs with an average of 69.50 including two centuries and two half-centuries.

Due to his performance, he was included in Wisden's Cricket World Cup Qualifier 2023 Team of the Tournament.

This achievement made him the fifth Sri Lankan batter to score 50 or more runs in three consecutive World Cup matches, joining the ranks of cricket legends like Kumar Sangakkara, Chamara Silva, Roshan Mahanama and Arjuna Ranatunga.

Pathum put unbeaten 137 run partnership with Sadeera Samarawickrama to bring 8 wickets victory for Sri Lanka.

[62] His unbeaten knock of 210 is also the highest individual ODI score in Sri Lankan soil surpassing the previous record of 169 held by Kumar Sangakkara.

He scored 118 runs from 101 deliveries and eventually Sri Lanka won the match by 7 wickets.

[64] He is the highest run-scorer in a three-match series for Sri Lanka and fourth overall with 346 runs with 173 average.

[67] In May 2024, he was named in Sri Lanka’s squad for the 2024 ICC Men's T20 World Cup tournament.