The Tamil Nadu diaspora (Tamil: அயலகத் தமிழர் (Ayalakat Tamiļar)) comprises people who have emigrated from South Indian state of Tamil Nadu, (and other adjacent Tamil speaking areas) to other non-Tamil Indian states and other countries, and people of Tamil Nadu descent (and other adjacent Tamil speaking areas) born or residing in other non-Tamil Indian states and other countries.

Many of Tamil emigrants who left shores of Tamil Nadu before 18th Century and mixed with countless other ethnicities. In medieval period Tamilians emigrated as soldiers, traders and labourers settled in Karnataka, Maharashtra, Sri Lanka, Thailand, Malaysia, Indonesia and intermixed well with local population, while few communities still maintain their language and culture. Many groups still claim descent from this era Tamil emigrants such as Kaikadis of Maharashtra, Thigalas, Hebbars of Karnataka, Velamas of Northern Andhra, Chittys of Malaysia, and few sections of Sri Lankan Tamils such as Sri Lankan Chetties, Bharatha people and Negombo Tamils.

During this period British, Dutch, French, Portuguese and Danish colony administrators recruited a lot of local Tamilians and took them to their overseas colonies to work as labourers, petty administration officers, clerical and military duties.

In the 19th century, Madras Presidency (of which the Tamil Nadu region was a core part of) faced brutal famines. Great Famine of 1876–78. Tamil Nadu was both politically and economically weak. Britishers thus made use of Tamil workers for their plantations to all over the world - significantly in Malaysia, Mauritius, South Africa, Sri Lanka (distinct from the Sri Lankan Tamils) and also as far as Fiji, Guyana, Trinidad.

Some of the Tamil groups (especially Chettiyars, Pillais, Muslims) emigrated as commercial migrants. These groups then dominated the trade and finance in primarily in Myanmar, Singapore, and other places. The first Indian to own a merchant ship during the British times comes from this group.

There is also a group of people from French India colonies of Pondicherry and Karaikal which emigrated and settled in other parts of the world, significantly in France and its overseas territories (or former territories) in the Indian Ocean, such as Réunion and Seychelles, and the French Caribbean islands of Martinique and Guadeloupe. They also settled in some other possessions of the French colonial empire, such as French Indochina (current-day Vietnam and Cambodia), where Tamil-speaking migrants from British India were also present.

These Tamilians well integrated, assimilated with their adopted countries, and became part and parcel of local populations in Mauritius, South Africa, Guyana, and Fiji. Where as Indian Tamils of Sri Lanka, and Tamil Malaysians of Malaysia were evolved into distinct ethnic nationalities of their own but retaining their ancestral language and religion in their new homelands.

In the second half of the 20th century, around 3.5 million Tamils emigrated from Tamil Nadu as skilled professionals, workers to various parts of India like Bangalore, Mumbai, Andaman Islands and also countries like UAE, USA, Singapore and so on. Some of them got citizenship of respective countries but still having strong family and cultural ties with Tamil Nadu, than those who migrated before 1950, who lost touch with their ancestral links in Tamil Nadu.