In 1923, Singh joined the National College in Lahore, where he not only excelled in academics but also in extra-curricular activities.[3] He was a participant of the dramatics society in the college.[3] By this time, he was fluent in Hindi, English, Urdu, Punjabi and Sanskrit languages.[3][26][27] In 1923, Singh won an essay competition set by the Punjab Hindi Sahitya Sammelan. In his essay on Punjab's Language and Script, he quoted Punjabi literature and showed a deep understanding of the problems of afflicting Punjab.[3] He joined the Indian nationalist youth organisation Naujawan Bharat Sabha (Hindi: "Youth Society of India") along with his fellow revolutionaries, and became popular in the organisation.[7] He also joined the Hindustan Republican Association,[25] which had prominent leaders, such as Ram Prasad Bismil, Chandrashekhar Azad and Ashfaqulla Khan. The name of the organisation was changed to Hindustan Socialist Republican Association at Singh's insistence.[8] A year later, to avoid getting married by his family, Singh ran away from his house to Cawnpore.[3] In a letter he left behind, he stated:
After killing Saunders, the group escaped through the D.A.V. College entrance, across the road.[35] Chanan Singh, a Head Constable who was chasing them, was fatally injured by Chandrashekhar Azad's covering fire.[35][37] They then fled on bicycles to pre-arranged places of safety.[35][38] The police launched a massive search operation to catch the culprits and blocked all exits and entrances[35][38] from the city; the CID kept a watch on all young men leaving Lahore.[35][38] They hid for the next two days.[35][38] On 19 December 1928, Sukhdev called on Durga Devi Vohra, their friend Bhagwati Charan Vohra's wife, for help, which she agreed to do.[35][38] They decided to catch the train departing from Lahore for Howrah (en route to Bathinda) early the next morning.[35][38] To avoid recognition, Singh shaved off his beard and cut his hair short.[39]