He served in the British Army during World War I. Chapin was born in Brooklyn, New York, in 1886.

[1] His parents divorced and his mother took the three-year-old Harold to live in England where he was educated and she continued her career.

[4] Chapin's acting career began at age seven when he first appeared publicly in a Frank Benson production.

[1][5] In December 1915 Alice Chapin, Calypso Valetta, Gerald du Maurier and Sydney Fairbrother appeared in a London memorial performance of four of his plays: The Philosopher of Butterbiggins, Innocent and Annabel, The Dumb and the Blind and It's the Poor that 'Elps the Poor.

Barrie wrote the introduction to a collection of Chapin's plays: The New Morality, Elaine, Art and Opportunity, and The Marriage of Columbine.