Madan Lal Dhingra was the sixth of seven children of a civil surgeon. All six sons studied abroad. In June 1906, Dhingra left Amritsar for Britain. He enrolled in University College, London, to study engineering.

Dhingra arrived in London a year after the foundation of Shyamaji Krishnavarma's India House. This organization in Highgate was a meeting place for Indian radicals. They had weekly meetings, which Dhingra would often attend. V. D. Savarkar became manager of India House and inspired Dhingra's admiration in the cult of assassination. However, Dhingra became aloof from India House and was known to undertake shooting practice at a range on Tottenham Court Road. On 1 July 1909, he attended an 'At Home' hosted by the National Indian Association at the Imperial Institute. At the end of the event, as the guests were leaving, Dhingra shot Sir Curzon-Wyllie, an India Office official, at close range. His bullets also hit Dr Lalcaca, a Parsee doctor, who was killed.

Dhingra was immediately arrested. At his trial, Dhingra represented himself, although he did not recognize the legitimacy of the court. He claimed that he had murdered Curzon-Wyllie as a patriotic act and in revenge for the inhumane killings of Indians by the British Government in India. He was found guilty and sentenced to death. He was executed at Pentonville Prison on 17 August 1909.

Udham Singh was a political activist from the Punjab. He was closely linked to communist activists and parties associated with the independence movement. During the early 1920s, after a brief three-month stay in Dover in 1921, he spent some time in the US, working in Detroit for the Ford Motor Company as a tool maker, before relocating to California. While in California, he established contacts with the Ghadar Party, which was dedicated to Indian freedom and independence. It had strong communist tendencies and was founded by South Asians living in America and Canada. He returned to India in 1927.

Back in the Punjab, Udham Singh was arrested for the illegal possession of firearms and sentenced to five years imprisonment. Singh was released from prison in October 1931. He managed to acquire a passport and made his way to London in 1934. In his application for his passport endorsement, he claimed to have been working as a sports outfitter in India, but since his arrival, living in Canterbury, Kent, he was unable to secure employment. There are suggestions that in this period he worked as a pedlar. During 1937, he worked as an extra in crowd scenes for Alexander Korda’s London Studios at Denham. During 1938, he worked as a carpenter at the RAF Station at Great Chessington, Gloucestershire, before becoming unemployed.

Udham Singh was well known in the Indian community at the time and also had contacts with Sikh pedlars living in Coventry, and Southampton. The objective of his stay in London was to find an opportunity to assassinate Michael O’Dwyer, the Governor of the Punjab in 1919, whom Singh held responsible for the Amritsar massacre, which had left a lasting impression on Singh after his brother and sister were killed there. Subsequently he had sworn to avenge the massacre. Singh had had a few opportunities to assassinate O’Dwyer but he was waiting for an occasion when his actions would have the most public impact.

On 13 March 1940, Singh shot O’Dwyer at a meeting of the East India Association and the Royal Central Asian Society at Caxton Hall. O’Dwyer was killed instantly and Lord Zetland, Lord Lamington and Louis Dane were also hit and wounded by the shots. Singh was immediately arrested and held in Brixton prison. There he staged a thirty-six day hunger strike, which resulted in him being forcibly fed through a tube. The assassination of O’Dwyer was reported widely in the press. In police statements and at court Singh gave his name as Mohamed Singh Azad as a symbol of Hindu-Muslim unity in the fight for Indian freedom. He was tried at the Old Bailey on 4 June 1940. Krishna Menon was part of his defence team. After a trial in which the prosecution presented a simple case and the defence of Singh was often sketchy and chaotic he was sentenced to death by hanging on 5 June and executed on 31 July at Pentonville Prison, where he was also buried. In 1974, his body was repatriated to India and cremated in his home village of Sunam.