[4] Growing up in Missouri, Mayfield played three years of junior varsity ice hockey at Webster Groves High School.

While competing with the 18U AAA St. Louis Amateur Blues, Mayfield won the overall skills competition of a 2009 national tournament.

[4] Following the tournament, Mayfield began to garner attention from scouts and he was drafted by the Indiana Ice of the United States Hockey League (USHL).

[5] Prior to starting his USHL career, Mayfield committed to play for the University of Denver Pioneers which compete in the Western Collegiate Hockey Association (WCHA).

[5] During the 2010–11 season, Mayfield was invited to participate in the NHL Research, Development and Orientation Camp and played for Team USA at the 2010 World Junior A Challenge.

While wearing jersey number 42, Mayfield played 17:04 minutes of ice time and recorded two shots and four hits.

[16] After making his NHL debut the previous season, Mayfield spent his second full professional campaign with the Sound Tigers.

[20] On April 9, Mayfield scored his first NHL goal in a 4–3 overtime loss against the Buffalo Sabres to help the Islanders qualify for the 2016 Stanley Cup playoffs.

[23] Following the signing, Mayfield accumulated two more points before suffering a lower-body injury during a 5–4 overtime loss to the Nashville Predators on February 6.

[27][28] Mayfield's older brother, Patrick, is a Major in the United States Air Force, and his younger sister Sarah is an interior designer.