Drafted into Royal Wahingdoh at 19 in 2011, Seityasen Singh repaid the trust reposed in him four years later when he helped the club gain promotion to the I-League in 2013-14. He scored his first I-League hat-trick against Salgaocar in May 2015. Seityasen's performances earned him a chance to play for India and he made his debut on June 11, 2015 against Oman in the 2018 FIFA World Cup Qualifiers. He impressed for the Highlanders in Hero ISL 2015, finding the back of the net once. He scored twice for them next season and there will be more expectations from him in the fourth edition of the league.