 After leaving the Army, Forbes engaged in construction work in the Pacific Northwest, moving to Seattle. He became active for the first time in state politics. He got married in Seattle to his wife Katherine and started a family having one daughter, Marcia. In 1912, Forbes and family moved to Hawaii, at that time a United States territory, and worked at the Pearl Harbor naval station as an engineer for the next five years. While in Hawaii, he served in four federal government appointments as Commissioner of Public Works, Chairman of the Public Service Commission, Chairman of the Harbor Commission and chairman of the Reclamation Commission appointed by President Woodrow Wilson. During this time in Hawaii, Forbes became acquainted with then Senator Warren G. Harding, who was on vacation with his wife at the time, a meeting that would eventually change both of their lives. His charismatic personality and hospitality created a positive impression with Harding, and soon the two became good friends. Forbes' wife became a close friend of Mrs. Harding.
