Davidson was born November 16, 1993, in Staten Island, New York, the son of Amy (née Waters) and Scott Matthew Davidson. His father was of mostly Jewish heritage and his mother is of Irish ancestry; Davidson was raised Catholic. He has a younger sister named Casey. His father was a New York City firefighter who died in service during the September 11 attacks; he was last seen running up the stairs of the Marriott World Trade Center, just before it collapsed. Davidson, then seven years old, was profoundly affected by the loss. He told The New York Times that it was "overwhelming" and that he later acted out in school as a result of the trauma; at one point, he ripped his hair out until he was bald. In October 2016, Davidson revealed on The Breakfast Club morning radio show that he struggled with suicidal thoughts when he was younger, and that the music of rap artist Kid Cudi saved his life.