2008-09: Matt Mahalak played for Culver Academies in Indiana. Mahalak was drafted in the second round, 33rd overall, of the 2009 OHL Priority Selection by the Plymouth Whalers.
2009-10: Played for the Youngstown Phantoms of the USHL. In 31 games for that team, Mahalak posted a 4.24 goals-against average and a .868 save percentage. His record was 9-17-3 for the season.
2010-11: Mahalak moved over to the OHL to join the Whalers. In 22 games for that team, Mahalak sported a 3.08 goals-against average and a .908 save percentage. He finished with a record of 8-8-1-3 on the season. In 2 playoff games for the Whalers, Mahalak posted a 3.00 goals-against average and a .913 save percentage.
2011-12: Mahalak appeared in 30 games for the Plymouth Whalers as a backup to starter Scott Wedgewood (NJD). He was 19-9 with 3 shutouts and had a 2.66 goals against and .923 save percentage. The Whalers finished first in the West Division and reached the second round in the playoffs. Mahalak appeared briefly in one playoff game in relief of Wedgewood; stopping the only shot he faced.