Medieval variant of Mervyn, resulting from the regular Middle English change of -er- to -ar-. Modern use may represent a transferred use of the surname derived from this in the Middle Ages. It is popular in the United States, where it is associated in particular with the American singer Marvin Gaye (1939–84) and the boxer Marvin Hagler (b. 1954).
Probably an altered spelling of French Tinel, a metonymic occupational nickname for a porter, from Old French tinel, an implement consisting of a pole with two chains on it, carried across the shoulders, with hooks on the ends of the chains, used for moving barrels and the like.