Nirankari (Punjabi: ਨਿਰੰਕਾਰੀ, lit. "formless one") is a sect of Sikhism. It was a reform movement founded by Baba Dyal Das in northwest Punjab in 1851. He sought to restore the practices and beliefs of Sikhs back to what he believed were prevalent when Guru Nanak was alive. This movement emerged in the aftermath of the end of Sikh Empire and the Sikh history after Ranjit Singh's death.

Nirankaris strongly oppose representing the "formless" God with any image, and believe that the true Sikh faith is based on nam simaran (remembering and repeating God's name). They believe in living hereditary gurus from Baba Dyal Das lineage, and that the Sikh scripture is an open text to which the wisdom of their living gurus after Guru Gobind Singh can be added. Nirankaris believe that a human guru to interpret the scripture and guide Sikhs is a necessity.

Nirankaris consider themselves to be Sikhs, and a part of Sikh history. Originally based in regions near their darbar in Rawalpindi, during the 1947 partition of India, they chose to leave the newly created Muslim-dominant Pakistan and migrated en-masse to India. In 1958, they established a new darbar in Chandigarh. Nirankari Sikhs are settled across contemporary India, with communities found from Srinagar to Kolkata.

The first half of the 19th-century saw Sikh power expanded with the Sikh Empire under Ranjit Singh. This strength was deeply admired and cherished by Sikhs.

The Nirankari sect was founded in 1851 by Baba Dyal, a Sahajdhari, who aimed at refocusing Sikhs on the Adi Granth – the Sikh scripture, and reform the beliefs and customs of the Sikhs. Baba Dyal's son and successor, Baba Darbar Singh, collected and recorded the Baba Dyal's essential teachings and established Nirankari communities outside of Rawalpindi. The Nirankari were estimated to number in the thousands by the time of the third leader of the movement, Sahib Rattaji (1870–1909). The Nirankari institution of biredars started, where the living Guru appointed his local representative to watch and lead local Nirankaris in distant towns and villages. The office of biredar has been a hereditary one in practice, states Webster.

In the 1891 Indian Census, 14,001 Hindus and 46,610 Sikhs identified themselves as Nirankaris. Under their fourth leader, Baba Gurdit Singh, some of the Nirankari took an interest in the Singh Sabha revivalist movement. The Nirankaris helped to bring the Anand Marriage Act of 1909 to the attention of the Sikh populace. The movement's fifth Guru, Sahib Hara Singh (1877–1971), started to reorganise the movement, and was later succeeded by his eldest son, Baba Gurbax Singh. Baba Jagdarshan Singh who succeeded Baba Gurbaksh Singh after his death in 1998, is the current Guru of the Nirankaris.

Nirankaris believe in a lineage of living Gurus, well beyond the ten accepted by Khalsa Sikhs. Like Khalsa, they too revere the Guru Granth Sahib, but consider it an open book to which the wisdom of the later and present-day living Gurus can be added.

The group later developed its own distinct spiritual movement. At the time of the partition of India in 1947, the Nirankari abandoned their center in Rawalpindi, which has since then been part of Pakistan, and established themselves on the Indian side of the partition.