Dewmi Vihanga was born on 2 August 2005. She emerged through Sri Lanka’s youth system and played domestic cricket for Chilaw Marians Cricket Club beginning around 2020-21. Early on, she also represented provincial sides such as Dambulla in Sri Lanka’s Super Provincial T20 tournament.

Her breakthrough at the international youth level came in 2023 when she was named in Sri Lanka’s squad for the inaugural Under-19 Women’s T20 World Cup. She stood out during that tournament and was selected in the “Team of the Tournament” for her consistent performances with the ball and useful contributions with the bat. In the U-19 circuit, she picked up wickets in several matches, including 3/11 against the USA and 2/22 versus South Africa, as well as scoring a half-century against Bangladesh.

In 2025, she was selected in the senior Sri Lanka Women's squad for the Tri-Nation ODI Series involving Sri Lanka, India, and South Africa. She made her ODI debut in May 2025 against South Africa. In that same series, she claimed her first five-wicket haul in ODIs, taking 5/43 against South Africa on 9 May. Across that tournament, she finished among Sri Lanka’s leading wicket-takers, collecting 11 wickets in 4 matches. Based on such consistent stints for the team, she found her place in the 2025 Women’s ODI World Cup as well.