Born in Sikkim, Thatal began playing competitive football in 2011 when he joined the Namchi Sports Academy of his native state.
After the U-17 World Cup, Thatal decided against joining the rest of his teammates with Indian Arrows, a development team which was to play in the I-League.
Aged 17 years and 132 days, Thatal became the youngest footballer to play an Indian Super League match.
After the merger of ATK and Mohun Bagan, Thatal signed a two-year contract on a permanent deal basis.
He made his debut for the club on 21 January 2021 at the 89th minute in their league match against Chennaiyin FC, winning 1–0.