Chosen in the 7th round of the 2008 Entry Draft (188th overall) by the Toronto Maple Leafs, he would make his NHL debut on March 11, 2015, recording 1 point in a 4–3 Toronto victory over the Buffalo Sabres. He was also named 3rd star of the game and went on to finish the season with the Toronto Maple Leafs, playing a total of 12 games. MacWilliam wore number 57 during his time with the Maple Leafs, becoming the first player in franchise history to wear the number.