The Los Angeles Times reports Mitchell sent a resignation letter Friday to Gov. Jerry Brown, saying she would step down immediately after six years on the powerful panel.
Commissioners are decision-makers for the land use agency, which oversees 1,100 miles of coastline.
Mitchell, a government affairs consultant and former legislative aide, was one of seven commissioners who voted in February to fire Executive Director Charles Lester, a 24-year veteran of the agency.
Mitchell and other panel members accused him of unspecified management issues and leadership problems. They declined to comment in detail because personnel matters are confidential.
Mitchell could not be reached for comment Friday.
CapRadio provides a trusted source of news because of you. As a nonprofit organization, donations from people like you sustain the journalism that allows us to discover stories that are important to our audience. If you believe in what we do and support our mission, please donate today.