Hailing from the coastal city of Galle, Pathum Nissanka's childhood was steeped in the challenges of a modest family background. His journey into the world of cricket began during his time at Kalutara Vidyalaya, later transitioning to Isipathana College in Colombo.

A defining moment arrived during a memorable clash in the School Cricket Championship. Facing off against President's College, Rajagiriya, at the Colts ground in Colombo, Nissanka etched his name in the annals of cricket history, hammering an unbeaten double century with 205 runs off a mere 190 deliveries. This standout performance marked the dawn of a promising career.

Nissanka's professional cricket debut occurred during the 2016–17 Districts One Day Tournament, representing Hambantota District. Subsequently, he ventured into the fast-paced world of T20 cricket, making his debut for Badureliya Sports Club in the 2017–18 SLC Twenty20 Tournament.

The pivotal moment in Nissanka's career unfolded in 2021 when he earned his maiden call-up to represent his country on the international stage. Making his debut against the West Indies, he left an indelible mark, particularly in Test cricket, by crafting a commanding century in the second innings. His innings of 103 runs marked him as the fourth Sri Lankan to achieve a century on Test debut, a milestone made even more remarkable as it was achieved away from home.

While his initial foray into ODI cricket posed challenges, Nissanka's fortunes changed dramatically after his maiden century against Australia in 2022. This marked the start of a prolific run in the 50-over format, highlighted by consecutive centuries during the ICC World Cup Qualifiers in 2023. With an impressive tally of 417 runs, including two centuries and two half-centuries, Nissanka played a pivotal role in Sri Lanka's World Cup qualification bid. At the main event, his consistency shone through as he amassed 332 runs in just 9 matches, earning himself a place among the elite as the fifth Sri Lankan to achieve three consecutive 50-plus scores in World Cup matches.

The year 2023 proved to be monumental for Nissanka as he etched his name in the record books by becoming the first Sri Lankan to surpass 1000 ODI runs in a calendar year. Carrying his form into 2024, he achieved another milestone by slamming a double hundred in the series against Afghanistan, becoming the first Sri Lankan batter to achieve this feat in ODIs. While he hasn't found the same success in T20 cricket yet, Nissanka remains hopeful of translating his ODI prowess into the shorter format.