History of Islam in India

Contrary to popular belief, Islam came to South Asia prior to Muslim invasions of India. Islamic influence first came to be felt in the early 7th century with the advent of Arab traders. Trade relations have existed between Arabia and the Indian subcontinent from ancient times. Even in the pre-Islamic era, Arab traders used to visit the Malabar region, which linked them with the ports of South East Asia. 
According to Historians Elliot and Dowson in their book The History of India as told by its own Historians, the first ship bearing Muslim travelers was seen on the Indian coast as early as 630 AD. H.G. Rawlinson, in his book: Ancient and Medieval History of India claims the first Arab Muslims settled on the Indian coast in the last part of the 7th century AD.
Shaykh Zainuddin Makhdum’s “Tuhfat al-Mujahidin” also is a reliable work.
This fact is corroborated, by J. Sturrock in his South Kanara and Madras Districts Manuals, and also by Haridas Bhattacharya in Cultural Heritage of India Vol. IV. It was with the advent of Islam that the Arabs became a prominent cultural force in the world. The Arab merchants and traders became the carriers of the new religion and they propagated it wherever they went.

In Malabar, the Mappilas may have been the first community to convert to Islam as they were more closely connected with the Arabs than others. Intensive missionary activities were carried out along the coast and a number of natives also embraced Islam. These new converts were now added to the Mappila community. Thus among the Mappilas, we find, both the descendants of the Arabs through local women and the converts from among the local people.

In the 8th century, the province of Sindh (in present day Pakistan) was conquered by an Arab army led by Muhammad bin Qasim. Sindh became the easternmost province of the Umayyad Caliphate.

In the first half of the 10th century, Mahmud of Ghazni added the Punjab to the Ghaznavid Empire and conducted several raids deeper into modern day India. A more successful invasion came at the end of the 12th century by Muhammad of Ghor. This eventually led to the formation of the Delhi Sultanate.
[Adapted from Wiki]