He first became active with the Westside Greens in the Santa Monica/West Los Angeles area in November 1988 and then joined his neighborhood Ocean Park Community Organization in early 1989.

Feinstein was first elected to the City Council in 1996 receiving 13,681 votes and finishing second amongst the thirteen candidates running for four seats.

Feinstein has also served on the Southern California Association of Government's Energy & Environment Committee (1997–2004), Growth Visioning Task Force (2001–2004), Regional Comprehensive Plan Task Force (2004–2008) and Integrated Policy Task Force (2009–2010), as well as the Westside Council of Governments, Local Government Commission (California), California League of Cities, National League of Cities, U.S. Conference of Mayors and International Council for Local Environmental Initiatives (ICLEI).

Feinstein has served in a variety of positions in the Green Party, on the local, county, state, national, international and global level.

Currently Feinstein writes a column called Inside/Outside on local politics for the Santa Monica Daily Press.