McDonald was selected by the Maple Leafs as the fourth overall pick in the 1973 NHL Amateur Draft and established himself as an offensive forward with three consecutive 40-goal seasons in Toronto in the mid-1970s. His trade to the Rockies in 1979 resulted in Toronto fans protesting the deal in front of Maple Leaf Gardens. He played parts of three seasons in Denver, before he was sent to Calgary in 1981 where he spent the remainder of his career. He co-captained the Flames to a Stanley Cup championship in his final season of 1988–89.