[4][3]: 463 The most commonly accepted theory of the origin of the Gallego is that it, like other small breeds of the northern part of the Iberian peninsula, descends from small dark-coloured horses introduced by Celtic immigrants in the sixth century BC.

[6] In the 1980s and 90s there was concern that the introduction of stallions of other breeds, with better meat-producing qualities, was placing at risk the original stock of Galician horses.

[8][9] The Gallego is regulated and protected by the Galician government,[10] in an attempt to increase the numbers of the feral stock.

It is present in the concellos of A Estrada, Cambados, Covelo, Poio, Pontevedra and Santa María de Oia in the province of Pontevedra; of Abegondo, Arzúa, Cambre, Cariño, Cerceda, Curtis, Ferrol, Irixoa, Lousame, Noia, Ortigueira and Porto do Son in the province of A Coruña; of Guitiriz, Muras, Ourol, Mondoñedo, Riotorto, Vilalba and Viveiro in the province of Lugo; and of Castro Caldelas, Coles and Lobios in the province of Ourense.

[8] Almost all Gallego horses are managed extensively, in semi-feral conditions on the mountains of Galicia.