Shortly after graduating St. John's College in 1810, Marriott was elected to the Maryland House of Delegates where he served on the Grievances and Courts of Justice Committee through the opening of the War of 1812.
During this time, Marriott built a log home on his plantation at Ivy Hill in Anne Arundel County.
[2] Marriott received a large undisclosed sum of money as an inheritance from his grandfather William Hammond including a slave named Hess Badger who was supposed to be manumitted, but remained a slave until Marriott's death.
In an 1854 case appealing his will, Hess' son Sam Badger appealed for his freedom from Marriott's heirs, since he was born into slavery while Marriott owned his mother, who was supposed to have her freedom before his birth.
[3] Marriott's law records are held at the New York Public Library archives.