Rajesh S was born in Pozhiyoor, a fishing hamlet at the southernmost tip of Kerala. His father and three brothers are fishermen. As a child, he was spotted by a localfootball coach who asked him to join the SMRC Pozhiyoor academy.
Rajesh made his professional debut on 27 October 2018 against Mohun Bagan after coming on as a substitute in the second half. He played a part in his team's equalising goal and later forced a fingertip save from the keeper. He scored his first I-League goal against Shillong Lajong on 11 November, registering a 3-1 win for his club. In the next game he scored the solitary goal in a 1-0 win over defending champions Minerva Punjab.