Lantos is a member of the Congressional Progressive Caucus and has repeatedly called for reforms to the nation's health-care system, reduction of the national budget deficit and the national debt, repeal of the Economic Growth and Tax Relief Reconciliation Act of 2001, and has opposed Social Security privatization efforts. He supports gay marriage rights and marijuana for medical use, is a strong proponent of gun control and is adamantly pro-choice.

Lantos is a well-known advocate on behalf of the environment, receiving consistently high ratings from the League of Conservation Voters and other environmental organizations for his legislative record. His long-standing efforts to protect open space have brought thousands of acres under the protection of the Golden Gate National Recreation Area, including Mori Point, Sweeney Ridge and - most recently - Rancho Corral de Tierra, which will keep its watersheds and delicate habitats free from development permanently. In 2005 he opposed an effort to expand public use of the Farallon Islands, a protected wildlife haven.

Lantos has consistently championed local transportation projects that need federal funds and, given his seniority in Congress, has proven highly successful at delivering this support.