Greenfield co-founded ice cream company Ben & Jerry's with Ben Cohen in a converted gas station in Burlington, Vermont, in 1978.

The company became known for its progressive social mission and activism.

• Ben & Jerry's was sold to Unilever in 2000 for $326 million, with an independent board retained to oversee its social mission.

• In September 2025, he resigned from Ben & Jerry's, saying the company's parent had stifled its independence and political activism.