Born in 1837, in a Punjab which was soon to fall into chaos as a result of courtly intrigue and murder, Thakur Singh was a mere child of six at the time of his father's death. As he grew up, he was given appointment by the British as extra-assistant commissioner for Amritsar district. He was also nominated a member of the Golden Temple managing committee. In this capacity, he observed how Sikh religion had been corrupted by the accretion of customs and rituals contrary to the teachings of the Gurus. He also felt concerned about. the general state of the Sikh community.

In 1873, occurred an event which gave a decisive turn to his career. Four Sikh pupils of the Mission High School in Amritsar declared their intention of abjuring their faith in favour of Christianity. Thakur Singh called in Amritsar a meeting of some of the leading Sikhs of the day, including Baba Sir Khem Singh Bedi, a descendant of Guru Nanak, Kanvar Bikrama Singh of Kapurthala, and Giani Gian Singh of Amritsar. This Sikh meeting laid the foundation of a society called the Sri Guru Singh Sabha.

Thakur Singh became the first president of the Singh Sabha. Apart from religious reform among the Sikhs, the Singh Sabha ushered in a new cultural consciousness in the Punjab. It aimed especially at the development of modern education. Thakur Singh remained at-the helm of affairs of the new society for a whole decade. He was a distinguished scholar of Persian and Punjabi, well versed in Indian as well as in Muslim lore. Because of his independent views, Thakur Singh was deprived of his position as extraassistant commissioner. In 1883, his estate was placed under a court. of wards. The same year he received from Maharaja Duleep Singh, living as a ranked British noble in London after being deprived of the throne of the Punjab, a wire inviting him.

Before his departure for England in 1884, Thakur Singh visited the Takhts, the principal Sikh shrines-at Amritsar, Anandpur, Patna and Nanded-to pray for the prosperity of Duleep Singh's cause. Accompanied by two of his sons, Narindar Singh and Gurdit Singh, a granthi or Scripture reader, Partap Singh, and three servants, he reached London, where he stayed as the guest of Maharaja Duleep Singh. He daily read out from the holy Guru Granth Sahib to the Maharaja and instructed him in the tenets of Sikhism. Under his influence, Duleep Singh determined to rejoin the faith of his forefathers.

In August 1885, Thakur Singh returned to the Punjab. Duleep Singh himself decided to return to his motherland and left England on 31 March 1886 to settle down quietly in Delhi. He invited Thakur Singh to meet him at Bombay and arrange for his reinitiation into Sikhism, but the government refused him permission to go to Bombay. Furthering the cause of Duleep Singh was now Thakur Singh's sole concern. To win support for him, he visited secretly the Indian princely states and the Sikh shrines. Major Evans Bell's book, The Annexation of the Punjab and the Maharajah Duleep Singh, exhibiting the illegality of British occupation of the Punjab, was widely circulated. Thakur Singh had the book translated into Punjabi by his friend Partap Singh, the granthi and published by another supporter, Diwan Butta Singh, of Aftab-i-Punjab Press.

Thakur Singh was now the most suspicious character in the eyes of the government. In intelligence reports and other government papers, he was described as "a troublesome person ... the friend and inciter of Duleep Singh." Yet he made good his escape into Pondicherry on 6 November 1886. His home in the Rue Law de Lauristan became the centre of activity against the British. Thakur Singh received correspondence from Duleep Singh through the French post office. Through the same medium he sent to him his letters and the Indian newspapers such as The Times of India and Madras Times. He laid out a fairly extensive system of communication in the Punjab, and had a continuous stream of visitors in Pondicherry including, occasionally, soldiers from the Indian Army.

Envoys came from Duleep Singh as well. From Russia, he sent to Thakur Singh a seal and letter in token of his appointment as prime minister to his emigre government. But the latter had not long to live. He suddenly fell ill and died on 18 August 1887. His ashes were taken to his ancestral village of Raja Sansi. His sons continued to live in Pondicherry, the eldest, Gurbachan Singh, receiving from Duleep Singh the title of prime minister.