[1] He was appointed adjutant of the Fourteenth Regiment of the Maryland Militia on April 18, 1798, and was commissioned captain on May 26, 1802.
He was a member of the Maryland House of Delegates from 1801 to 1803 and 1805, and served as speaker in the latter year.
During the Eleventh Congress, he was chairman of the Committee on the District of Columbia.
Van Horne was again elected to the Maryland House of Delegates and served from 1814 to 1816.
[2] After his death his house located at 4706 Mann St. just outside Washington, D.C. is believed to have been a station on the Underground Railroad.