He voiced Roger in the Ice Age franchise, and numerous characters in the shows Bob's Burgers, Robot Chicken and BoJack Horseman.

He briefly attended college at the University of Wisconsin, but dropped out after earning a 0.67 GPA his freshman year.

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 a featured role in When Do We Eat?, as an Internet tycoon who, after losing his fortune, becomes a Hasidic Jew.

[12] On November 8, 2018, it was announced that Greenfield was set to reprise his role as Leo D'Amato in the 8-episode revival series of Veronica Mars.

[14] Greenfield has worked with Young Storytellers Foundation on numerous occasions, stating that his own kids have inspired him to help children find self-confidence and creativity.