Ranjit Singh was the only child of Maha Singh, on whose death in 1792 he became chief of the Shukerchakias, a Sikh group. His inheritance included Gujranwala town and the surrounding villages, now in Pakistan. At 15 he married the daughter of a chieftain of the Kanhayas, and for many years his affairs were directed by his ambitious mother-in-law, the widow Sada Kaur. A second marriage, to a girl of the Nakkais, made Ranjit Singh preeminent among the clans of the Sikh confederacy.

In July 1799 he seized Lahore, the capital of the Punjab. The Afghan king, Shah Zaman, confirmed Ranjit Singh as governor of the city; in 1801, however, Ranjit Singh proclaimed himself maharaja of the Punjab. He had coins struck in the name of the Sikh Gurus, the revered line of Sikh leaders, and proceeded to administer the state in the name of the Sikh commonwealth. A year later he captured Amritsar, the most important commercial entrepot in northern India and sacred city of the Sikhs. Thereafter he proceeded to subdue the smaller Sikh and Pashtun (Afghan) principalities that were scattered over the Punjab. But his later forays east were checked by the English, with whom he signed the Treaty of Amritsar (1809) fixing the Sutlej River as the eastern boundary of his territories.

Ranjit Singh then turned his ambitions toward the north and west, against the Pashtuns. In the summer of 1818 his troops captured the city of Multan and six months later entered the Pashtun citadel, Peshawar. In July 1819 he finally expelled the Pashtuns from the Vale of Kashmir. By 1820 he had consolidated his rule over the whole Punjab between the Sutlej and the Indus rivers.

All of Ranjit Singh's conquests were achieved by Punjabi armies composed of Sikhs, Muslims, and Hindus. His commanders were also drawn from different religious communities, as were his Cabinet ministers. In 1820 Ranjit Singh began to modernize his army, using European officers to train the infantry and artillery. The modernized Punjabi army fought well in campaigns in the North-West Frontier (on the Afghanistan border). Ranjit Singh added Ladakh (a region of eastern Kashmir) to his kingdom in 1834, and his forces repulsed an Afghan counterattack on Peshawar in 1837.

In 1838 he agreed to a treaty with the British viceroy Lord Auckland to restore Shah Shoja' to the Afghan throne at Kabul. In pursuance of this agreement, the British Army of the Indus entered Afghanistan from the south, while Ranjit Singh's troops went through the Khyber Pass and took part in the victory parade in Kabul.

Shortly afterward Ranjit Singh was taken ill, and he died at Lahore in June 1839, exactly 40 years after he had entered the city as a conqueror. In little more than six years after his death, the Sikh state he had created collapsed because of the internecine strife of rival chiefs.