Jat Sikh or Jatt Sikh (Punjabi: ਜੱਟ ਸਿੱਖ, pronounced [d͡ʒəʈːə̆ sɪkːʰə̆]) is an ethnoreligious group, a subgroup of the Jat people whose traditional religion is Sikhism, originating from the Indian subcontinent. They are one of the dominant communities in Punjab, India, owing to their large land holdings. They constitute a substantial proportion of the Sikh population.

The New Indo-Aryan term jaṭṭ descends from the Prakrit form jaṭṭa, itself from jarta, or jartika, the name of a tribe stated in antiquity as residing in Vahlika.

Initially, some Jats started to follow the teachings of Guru Nanak, which did much to remove social barriers created by the sāvarṇa caste society. Jats were previously indifferent towards deep religious affairs.

While followers important to Sikh tradition like Baba Buddha were among the earliest significant historical Sikh figures, and significant numbers of conversions occurred as early as the time of Guru Angad (1504–1552), the first large-scale conversions of Jats is commonly held to have begun during the time of Guru Arjan (1563–1606). While touring the countryside of eastern Punjab, he founded several important towns like Tarn Taran Sahib, Kartarpur, and Hargobindpur which functioned as social and economic hubs, and together with the community-funded completion of the Darbar Sahib to house the Guru Granth Sahib and serve as a rallying point and center for Sikh activity, established the beginnings of a self-contained Sikh community, which was especially swelled with the region's Jat peasantry. They formed the vanguard of Sikh resistance against the Mughal Empire from the 18th century onwards. While W. H. McLeod was of the position that Jats only began to convert in large numbers to Sikhism and influence the community by the time of Guru Amar Das and certainly by the time of Guru Arjan, Pashaura Singh and Louis E. Fenech on the other hand opine that large scale conversions of Jats into Sikhism came about during Guru Nanak's time settled down in Kartarpur and living an agricultural lifestyle.

When Guru Arjan compiled the Adi Granth, three verses (in Asa and Dhanashree ragas) attributed to Bhagat Dhanna (born 1415), a Jat, were included in the scripture.

It has been postulated, though inconclusively, that the increased militarisation of the Sikh panth following the martyrdom of Guru Arjan (beginning during the era of Guru Hargobind and continuing after) and its large Jat presence may have reciprocally influenced each other.^{[full citation needed]}

Dharam Singh, one of the inaugural Panj Piare quintet, was a Jat. 18th century Sikh literature claims he was the reincarnation of Bhagat Dhanna.

At least nine of the 12 Misls of the Sikh Confederacy were led by Jat Sikhs, who would form the vast majority of Sikh chiefs. Of the remaining three misls, the Ahluwalias were led by Kalals who claimed descent from Jats, the Ramgarhia Misl was founded by both Tarkhans and Jats, and the Dallewalia Misl was founded by both Khatris and Jats. According to W. H. McLeod, the Jat Sikhs dominated the Sikh Confederacy during the 18th century. The Jat states of the 18th century conducted marital alliances with one another, such as between the Sukerchakias and Jind.