Robert Mills (1781-1855) was born in 1781 in Charleston, South Carolina. As a teenager he studied pattern-books and learned the basics of drafting, and in 1800 he moved to Washington, DC, to work in the office of architect James Hoban. There he met President Thomas Jefferson who recommended Mills to Benjamin Latrobe. He was a pupil and assistant to Latrobe in Philadelphia until 1808, working on many architectural and engineering projects.
In 1808 Mills married Eliza Barnwell Smith and established his architectural practice in Philadelphia, receiving many major commissions. From 1815 to 1819 Mills lived with his family in Baltimore, Maryland, overseeing the construction of his commission for the Washington Monument in Baltimore. He also worked on several engineering projects in the city. After construction halted in 1819 due to an economic depression, he moved to South Carolina to become the Acting Commissioner of the Board of Public Works. In 1823 his position was abolished due to rising project costs, but he continued to work on individual commissions, and also published several books and pamphlets on South Carolina and engineering.
In 1830 Mills and his family moved to Washington, DC. There he directed alterations and restorations of the White House, Executive Offices, and the Capitol. After establishing himself with these projects he received many more commissions and was appointed Architect of the Federal Buildings. During this time his design for the Treasury Building was adopted, and he oversaw the construction of the U. S. Patent Office - now the Smithsonian Institution's Donald W. Reynolds Center for American Art and Portraiture - and the Old Post Office, among other projects. His federal office was abolished in 1842, but Mills continued to work on independent building projects. In 1845 his plan for the Washington Monument in Washington, DC, which he had designed in 1833, was adopted and construction began in 1848. He lived in Washington, DC, until his death in 1855.