At age 19, Coiro got his first professional gig as an understudy to three roles in the American premiere of Conor McPherson's off-Broadway play This Lime Tree Bower. After graduating from CMU, Coiro landed the role of Eddie the Bellhop in the Lincoln Center revival of George S. Kaufman's Dinner at Eight. Coiro then moved to Los Angeles and landed his first on-screen role as Billy Walsh on Entourage. The role meant to be a guest star but soon evolved into an iconic character that has defined Coiro's career.