During an interview with CNN, the 70-year-old veteran star said, "I wanted to vote for somebody who, in some way, is concerned about the things that concern me.
"After my experience, it's very clear to me that the DNC (Democratic National Convention) is gone, and we need a progressive party."
Sarandon also said she still admires former primary rival Bernie Sanders, whom she previously supported.
The actress's comments came in the wake of the controversy surrounding the Dakota Access Pipeline project, the issue that has seen many celebrities and environmentalists protest.