Justin McCarthy was born in Hazleton, Pennsylvania, and lived in Weatherly most of his life. His family was affluent and he was exposed to quality museum art at an early age. He experienced tragedy with the death of his brother in 1906, and his father in 1907. During his second year in law school, McCarthy suffered from a severe mental breakdown after failing an exam. He spent five years in a mental institution. There, he began to draw and paint at the encouragement of his mother. He painted subjects from everyday life and many figures from popular culture, most notably female movie stars and celebrities, as he was an introvert and too shy for courtship in real life. McCarthy mostly created art with pencils and watercolors on paper, but later in his life he experimented with oil painting. He is a highly regarded American naive artist, with work exhibited in many museums around the country.