He was born in Tervola, Finnish-Lapland, on 2 December, 1813. He matriculated in 1830 and initially studied Oriental languages, but continued his studies in Finnish folk poetry. In 1836 he completed his Master’s Degree at the University of Helsinki. Castrén made his first expedition to Lapland in 1838 under the direction of C. R. Ehrström, the regional doctor. The following year he travelled to Finnish and Russian Karelia, where he collected language and ethnographic materials for interpretation of the Kalevala, and wrote his dissertation on the relationship of the Finnish, Estonian and Saami nominal paradigms, De affinitate declinationum in lingua Fennica, Esthonica et Lapponica.

In 1840 Castrén was appointed docent of Finnish and other Nordic languages. His Swedish translation of the Kalevala was completed in 1841. His expedition to Norwegian, Finnish and Russian Lapland accompanied by Elias Lönnrot took place in the winter of 1841–1842. On the Siberian Expedition organised by the St. Petersburg Academy in 1842–1844, Castrén acted as a language specialist, collecting Nenets (Samoyed) and Komi (Zyrian) materials. In 1845 Castrén published his research work Om Accentens inflytande i Lappska Språket (A phonetic history of the Saami language), he completed a grammar of the Komi (Zyrian) language and began his study of the Mari (Cheremis) language. Castrén’s most extensive expedition was conducted from 1845–1849, which he made via Kazan to the Samoyeds in Siberia. During his travels he finished work on the Mari grammar, studied the Khanty (Ostyak) people and language, the Tatars, the Evenki and Buryats, and finally arrived in China.

M. A. Castrén was married to Natalia Tengström in 1850. The following year saw the birth his only child Robert, and Castrén was appointed the first Professor of the Finnish language at the University of Helsinki. This position he held only briefly; Castrén passed away on 7 May, 1852.