He was a tough player at nearly six feet.He was brought in Calcutta giants Mohun Bagan by then head coach Arun Sinha, and signed for the club in 1959.

His performance against East Bengal in a match of the Kolkata Derby in 1968, was highly praised by one of India's oldest newspaper Amrita Bazar Patrika.

[16][10] Singh was also part of the Mohun Bagan team that toured to East Africa and played matches in Uganda, Kenya, Zanzibar and Tanganyika.

[19] Singh represented India under management of the coach Syed Abdul Rahim,[20][21] during the "Golden age" of Indian football.

[25] In the final, Rahim showcased his brilliance, deploying injured Singh as centre forward.

[20] According to P. K. Banerjee, Jarnail used to play as a centre-forward in his college days and Rahim's research helped the team surprise the opponent, a 2–1 victory over South Korea.

In the same year, he went on to play for his country at the 1964 AFC Asian Cup, where they also finished as runners-up as Israel won the trophy.

Singh took charge of India and managed the team in 1969 Merdeka Cup,[29] and 1970 Singapore Friendship Tournament.

When he was in Lyallpur (now Faisalabad in Pakistan) in 1948, the place was burning due to political madness, and many of his family members were killed.

[11] Jarnail's son Jagmohan Singh was also a professional footballer who played for India as a defender and participated in 1993 SAARC Gold Cup in Pakistan.

It was almost impossible to beat him in a one-on-one situation, not even Chunni da (Chuni Goswami) could do it.In memory of Singh, the I-League "Best Defender Award" is renamed as "Jarnail Singh Award", given to the best defender in each season by the All India Football Federation (AIFF), in collaboration with Football Players' Association of India.