Is the Stock Market Open on Martin Luther King Jr. Day? Martin Luther King Jr. Day celebrates the memory of one of the greatest civil rights activists of the last century. Author: Jan 15, 2021 8:58 AM EST Martin Luther King Jr. Day was first signed into law in 1983, and first officially observed as a holiday in 1986. Generally observed on the third Monday of January (close to or on King's actual birthday, January 15), MLK Day celebrates the life and legacy of one of America's most well-known and influential activists, who fought for racial and economic justice across the country. Martin Luthe...