Previously strongly Republican, Imperial County is now a Democratic stronghold in presidential, congressional and local elections. The last Republican to win a majority in the county was George H. W. Bush in 1988.

On November 4, 2008, Imperial County voted 69.7% for Proposition 8, which amended the California Constitution to ban same-sex marriages, showing more support for the proposition than any other strongly Democratic county. After Prop 8 was declared unconstitutional by a lower federal court, Imperial County continued to defend Proposition 8 in the federal judicial system. However, on February 6, 2012, the United States Court of Appeals for the Ninth Circuit denied Imperial County legal standing in the case Hollingsworth v. Perry.

Imperial County is in California's 51st congressional district, represented by Democrat Juan Vargas. In the state legislature, the county is in the 56th Assembly District, represented by Democrat Eduardo Garcia,[54] and the 40th Senate District, represented by Democrat Ben Hueso.