Born at the Montpelier estate near Hagerstown, Maryland, Mason was educated by a private tutor and graduated from Princeton College in 1836. He studied law, was admitted to the bar, and commenced practice in Hagerstown in 1838.
He later served as a member of the Maryland House of Delegates in 1838 and 1839, and was elected as a Democrat to the Twenty-seventh Congress, serving one term from March 4, 1841 to March 3, 1843. He was a judge of the Maryland Court of Appeals from 1851 to 1857, and afterwards a collector of customs at Baltimore, Maryland, from 1857 to 1861. He moved to Annapolis, Maryland, and served as Secretary of State of Maryland from 1872 until his death in 1873. He is interred in Rose Hill Cemetery of Hagerstown.