Al Millar grew up playing minor hockey in Winnipeg and starring with the Winnipeg Canadians of the MJHL at the age of 18 where he went 10-4-2 with a 3.80 GAA. He then played one year of major junior hockey in the QJHL with the St. Hyacinthe Flyers and the Montreal Nationale.
After playing semi-pro hockey with Quebec in the QSHL, where he was a Second Team All-Star in 1949-50, goalie Al Millar signed his first professional contract with the New Haven Ramblers of the AHL on September 17, 1950. Just three months later he inked a deal with the Kansas City Royals of the USHL. Just one month later he was dealt to the Portland Eagles of the PCHL for Wally Bak.
After a season with Shawinigan Falls of the QSHL and the Charlottetown Islanders of the Maritime League, Millar began a three-year stint with the Quebec Aces. In 1957-58 he was called up to the NHL by the Boston Bruins where he played in six games. He also played 25 games with the Quebec Aces and Springfield-Buffalo of the AHL.
Millar never returned to play again in the NHL but he did continue to play professionally in the minors for another 12 years with an assortment of teams including the Seattle Totems and Victoria Maple Leafs of the WHL and finally the Rochester Americans in 1969-70. Millar played a total of 20 professional seasons in goal including the six games in goal for the Boston Bruins where he had a 1-4-1 record with a 4.17 GAA.