Sukhdev Thapar was born on 15 May 1907 in the Naughara area of Old Ludhiana in the Punjab Province of British India, into a Punjabi Khatri family. His father, Ramlal Thapar, died when Sukhdev was still young. After his father's death, he was raised by his uncle, Lala Achintram, who became a guiding influence in his life.

From a young age, Sukhdev was immersed in the rising nationalist sentiment sweeping across India. Like many educated youth of the time, he grew increasingly disillusioned with British colonial rule. His formal education introduced him to ideas of revolution, resistance, and the role of youth in achieving political change. His political awareness took root early, and he joined organizations that were actively challenging the British Empire.

He became deeply involved with the Naujawan Bharat Sabha, a youth revolutionary group dedicated to spreading anti-colonial ideals among the Indian masses. He helped organize lectures, distribute pamphlets, and cultivate a network of young, idealistic minds committed to India’s freedom. His ideological conviction eventually led him to the Hindustan Socialist Republican Association (HSRA), where he quickly rose to prominence.

Within the HSRA, Sukhdev became the chief of the Punjab unit, responsible for executing plans, organizing revolutionary cells, and mentoring younger recruits. He believed in socialist principles and held strong convictions about the need for armed resistance as a legitimate path to independence.

In late 1928, the Simon Commission, a British-appointed political delegation without a single Indian member, arrived in Lahore. Its presence sparked protests across the country. One of the most vocal critics, Lala Lajpat Rai, led a peaceful march in opposition to the Commission on 30 October 1928. The march, however, turned violent when police, under the order of Superintendent James Scott, charged the crowd with batons. Rai was badly injured and succumbed to his wounds two weeks later.

The news of Rai’s death devastated the nationalist movement. For Sukhdev Thapar and his associates in the HSRA, it demanded vengeance. The group, including Bhagat Singh and Shivaram Rajguru, resolved to assassinate Superintendent James Scott to avenge Rai’s death. However, on 17 December 1928, in a tragic case of mistaken identity, they killed John Saunders, an assistant superintendent, believing him to be Scott. Sukhdev played a central role in the planning of this attack.

As Saunders exited the police station on his motorcycle, he was shot by Rajguru and fatally finished off by Bhagat Singh. During their escape, Head Constable Channan Singh was also shot and killed by Chandrashekhar Azad, who was covering the retreat. The assassins fled Lahore immediately, changing identities and dispersing across cities.

While Singh and Rajguru went underground, Sukhdev continued his revolutionary work and was actively involved in strategizing for the group. When Singh and Dutt resurfaced months later during the symbolic bombing of the Central Legislative Assembly in April 1929, it reignited the investigation into Saunders’ murder. Evidence from arrests and confessions linked Sukhdev directly to the conspiracy.

He was arrested in April 1929, following a First Information Report filed by Hamilton Harding, where he was named the primary accused in what would become the Lahore Conspiracy Case. Listed as "Swami alias Peasant, son of Ram Lal," Sukhdev faced a court that had already made up its mind. Alongside Bhagat Singh and Rajguru, he was charged with conspiracy to murder and waging war against the British Crown.

Despite public support and multiple appeals, including ones from Mahatma Gandhi and other Congress leaders, the British government stood firm. On 7 October 1930, the special tribunal declared all three guilty and sentenced them to death.

The executions were scheduled for 24 March 1931, but in a covert decision, they were moved ahead to the evening of 23 March 1931, likely to prevent public protests. The three were hanged at 7:30 PM in Lahore Central Jail, and their bodies were cremated in secrecy at Hussainiwala, near the banks of the Sutlej River.