Greenfield began pursuing an acting career in 1998 after he graduated from high school. He landed guest appearances on dramas such as "Boston Public", "Gilmore Girls" and "The O.C." Greenfield scored his first lead role on the short-lived series "Modern Men" as one of three bachelors who hire a life coach to help them understand women. Greenfield had more success in supporting roles on "Veronica Mars" (reprising the role in the film adaptation in 2014) and "Greek". In 2007 he landed a recurring role on "Ugly Betty". He made other guest-starring appearances on the remake of "Melrose Place", the short-lived "No Ordinary Family", and "Castle".