Before starring on The Real O'Neals, he also appeared off Broadway at theaters such as the Signature, Playwrights Horizons, MCC, The Vineyard, The Public, The Culture Project, The Flea, The Wild Project, New York Theater Workshop, the Barrow Street Theater, Rattlestick, Ensemble Studio Theater, and many others. He is a recipient of Audio file Magazine's Earphones Award for his narration of Hollis Seamon's novel Somebody Up There Hates You. His other audiobook work includes Perks of Being a Wallflower, Matthew Quick's Forgive Me, Leonard Peacock, and more. Additional credits include the celebrated short films Promised Land and Welcome to the Wayne. He currently lives in the two cities, New York City, New York, and Los Angeles, California.
Galvin was born and raised in Katonah, New York. In his early teenage years, Galvin was asked by his mother, Abbie (née Fink), several times if he was gay. He came out to her when he was fourteen. Galvin has two siblings. His father is Catholic and his mother is Jewish; he was raised "both Jewish and Catholic going to CCD, Hebrew School and church", and has described himself as Jewish. In June of 2016 Galvin ignited a controversy when, in an interview with Vulture, he accused Eric Stonestreet of Modern Family of perpetuating stereotypes through caricature (though conceding Stonestreet's acting talent), ridiculed an interview that Colton Haynes had with Entertainment Weekly, and accused director Bryan Singer of preying on underaged boys.