John Mateer was born on December 4th, 1995 in Mineola, New York to John and Carol Mateer. Mateer is one of four children.

Mateer lost both of his parents to cancer when he was still a minor and he moved to New York City from his childhood home on Long Island directly out of high school. Attending CUNY Queens College, Mateer began to study film at the undergraduate level before transferring to CUNY Hunter College in the fall of 2016 to pursue a degree in politics and government.

Mateer is openly gay and he frequently references the struggles of being LGBT in his lyrics.