McRuer was born 1826 in Bangor, Maine. He moved to San Francisco, California, in 1851 during the California Gold Rush and entering the business of a commission merchant. He was a member of the San Francisco Board of Education in 1859 and 1860.
During the Civil War McRuer was a member of the United States Sanitary Commission. He was elected as a Republican to the 39th United States Congress (1865–1867), but did not run for reelection. McRuer traveled in Europe for two years, then returned to San Francisco. After his return he served as harbor commissioner for four years and served on the board of directors of the Security Savings Bank of San Francisco.
McRuer died 1898 in Saint Helena, California and is buried in Saint Helena Public Cemetery.