It is currently represented by Democrat Steve Padilla of Chula Vista.

The district stretches along the Mexico–United States border and predominantly includes rural Imperial Valley and areas of California along the Colorado River, including Needles, Blythe, and Indio.

However, most of the district's population is in southern San Diego County, including Imperial Beach, Otay Mesa, Chula Vista, National City, Lincoln Acres, Bonita, the Tijuana River Valley, and the southeastern side of San Diego.

Due to redistricting, the 18th district has been moved around different parts of the state.

The current iteration resulted from the 2011 redistricting by the California Citizens Redistricting Commission.