Arnold & Porter's Washington, DC office is the largest and oldest within the firm. It was founded in 1946 on the experience and values with which the firm built its reputation, including a solid foundation of regulatory and knowledge of, and experience working within, the inner machinery of the US government and its agencies.

From that tradition, the office expanded to include many areas of corporate law into its interdisciplinary practice, including antitrust, bankruptcy, compensation and benefits, consumer product safety, corporate and securities, employment law, environmental, financial services, government contracts, information security and privacy, intellectual property, international trade, litigation, product liability, public policy/legislative, real estate, securities enforcement and litigation, tax, and telecommunications.