c. 1400, "avowal, pledge, solemn declaration," from Old French protest (Modern French prôtet), from preotester, and directly from Latin protestari "declare publicly, testify, protest," from pro- "forth, before" (from PIE root *per- (1) "forward," hence "in front of, before") + testari "testify," from testis "witness" (see testament). Meaning "statement of disapproval" first recorded 1751; adjectival sense of "expressing of dissent from, or rejection of, prevailing mores" is from 1953, in reference to U.S. civil rights movement. First record of protest march is from 1959.
mid-15c., "to declare or state formally or solemnly," from Old French protester, from Latin protestari "declare publicly, testify, protest" (see protest (n.)). Original sense preserved in to protest one's innocence. Related: Protested; protesting.