Win Htet Oo first took up swimming when he was six years old and grew up to be a professional swimmer. He represented Myanmar in international tournaments such as the 2013 and 2019 Southeast Asian Games.[4] In 2017, he moved to Melbourne, Australia to get better training.[5] He also held the national record for the 50 metres, 100 metres and 200 metre men's freestyle events.[2] He also swam for the collegiate team of New York University.[3]
Following the 2021 Myanmar coup d'état, Win Htet Oo decided to forego competing in the 2020 Summer Olympics in April 2021 as a protest against the military junta which assumed power in Myanmar and after learning that the Myanmar Olympic Committee (MOC) fell under the military's control.[2] In March 2021, he made a petition to the International Olympic Committee for the expulsion of the MOC from the Olympic movement and that athletes from Myanmar to be able to compete as neutral athletes, but both requests were denied.[4][6] The IOC also remarked that "to the best of our knowledge" that Win Htet Oo has not been selected to be part of the Myanmar delegation at the Olympics.[5]