Hanifin was to be a top-three pick for the 2015 NHL Entry Draft, and the number-one rated defenseman. He was picked fifth overall by the Carolina Hurricanes. Hanifin played for the USA Hockey's U17 program based out of Ann Arbor, Michigan, but was added to the U18 national team as an underage player, helping to lead Team USA to the gold medal at the 2014 IIHF World U18 Championships. He was the highest-scoring American defenseman of the tournament with one goal and five points. After fast-tracking his high school graduation, Hanifin matriculated at Boston College as a 17-year-old, playing for the Eagles and becoming the second-youngest player in the team's history.