The History of Martin Luther King Jr. Day MLK Day is always celebrated on the third Monday of January and this year, it happens to be on the same day as his birthday, Jan. 15. The national holiday marks the birthday of the civil rights legend. The campaign to create the holiday to honor King began after his assassination in 1968. While President Reagan signed the holiday into law in 1983... it only started to be observed three years later. In 2000, all states observed the holiday for the very first time.