2009-10: Merrick Madsen played for the California Heat Bantam AA hockey program in the Los Angeles area.
2010-11: Madsen skated for the California Heat midget U16 AAA team.
2011-12: Merrick Madsen moved from the West Coast to New Hampshire to play prep school hockey at the Proctor Academy. A sophomore for the Hornets, he shared the goaltending duties with freshman Beau Collins, Madsen posted a 6.42 goals against and .862 save percentage for a team that finished 7-20-0. Madsen participated in USA Hockey's Warren Strelow National Goaltending camp and the Select 17 Development Camp in June.
2012-13: Madsen committed to playing college hockey at Harvard in 2014-15 in July before returning to Proctor Academy for his junior season. While Proctor again struggled in New England prep league play, finishing 9-16-3, Madsen had a strong season, recording a 3.74 goals against and .905 save percentage in nearly 1200 minutes of ice time. He was selected by Des Moines in the second round (18th overall) of the 2013 USHL Entry Draft. Madsen was ranked 26th amongst North American goalies in Central Scouting's final rankings and was selected by Philadelphia in the sixth round (162nd overall) in the 2013 NHL Draft.