"I strongly condemn the killing of RSS leader Ravinder Gosain in Ludhiana. Violence is unacceptable. The guilty must be brought to book," Mr Gandhi wrote on Twitter.
Ravinder Gosain, 60, was returning home after attending an RSS Sakha in the morning when two motorcycle-borne assailants shot him and fled. Mr Gosain died on the spot. The attack had happened in the Kailash Nagaar locality of Ludhiana.
A three member Special Investigation Team (SIT) led by Deputy Commissioner of Police Gagan Ajit Singh has been formed to probe the case.
Yash Giri, city secretary of the RSS, had condemned the incident and said it was "definitely a target killing".
Union Home Minister Rajnath Singh had also raised the issue with Punjab Chief Minister Amarinder Singh, who assured him of quick action.