After a stage with St-Michaels, the Toronto Maple Leafs OHA affiliate, Mackell began his National Hockey League career with the Toronto Maple Leafs in 1948. The majority of his career was spent with the Boston Bruins where he would retire following the 1960 season. MacKell won two Stanley Cups with the Maple Leafs in 1949 and 1951. After winning his 2nd Stanley Cup with the Leafs, Fleming David Mackell was traded by Toronto to the Boston Bruins in return for young defenceman Jim Morrison. In Boston, he attained NHL First All Star Team status for the 1952-53 season, at the position of center, playing on a line composed ofEd Sanford and Johnny Peirson. Flem Mackell also won the Elizabeth C. Dufresne Trophy in 1953, awarded annually to the outstanding Bruins player on Boston Gardens home ice. He was named an alternate captain of the Boston Bruins in 1955. Flem Mackell became a mainstay and catalyst of Boston's strong and prolific offense of the late 1950s. In 1956-57, he centered a line composed of veteran iron manCal Gardner and Rookie Of the year, Calder trophy winner Larry Regan. Along with later Bruins` linemate, Don McKenney, Fleming Mackell led all scorers during the epic 1957-58 Stanley Cup playoffs. In the spring of 1959, Fleming Mackell led the Boston Bruins against the New York Rangers on an exhibition tour of Europe. A rugged, hard charging playmaker with a razor sharp skating style, he was a side of the net scoring specialist. The versatile Flem MacKell frequently played at left wing, principally with Don McKenney and Jerry Toppazzini, a trio whose production matched the output of the vaunted UKE Line, along with his regular position at centre. Fleming MacKell often assumed a defensive checking role, he was the catalyst of the short lived Hustle line in 1959-60. Upon his retirement from the Boston Bruins & the NHL at the conclusion of the 1959-60 season, Fleming MacKell briefly became Player/Coach for the Quebec Aces of the AHL in 1960-61. He approached the Detroit Red Wings for a tryout in September 1961 and appeared in some exhibition games, but did not make the club. He is the son of former NHL player Jack MacKell of the original Ottawa Senators. His daughter JoAnne is an established country rock singer based in Toronto. Mackell died on October 19, 2015.