Admitted to the Virginia bar, Grigsby had a private legal practice near Norfolk, but his growing deafness caused him to turn to journalism. For six years he owned and edited the Norfolk
American Beacon. He succeeded Albert Allmand as Norfolk's sole delegate in the Virginia General Assembly, and won election in his own right the following year (so served), and (following the death of an elected delegate) became one of his Tidewater district's delegate to the
Virginia Constitutional Convention of 1829–1830. Although some delegates proposed allowing for the gradual abolition of
slavery in Virginia,
Nat Turner's slave rebellion had just been suppressed, so that proposal was quickly tabled by
Tidewater representatives including Grigsby and his colleagues, although the constitution did allow western Virginians additional representatives in the Virginia General Assembly. Decades later (after the American Civil War and the creation of the state of West Virginia), Grigsby would publish a history of that convention, which would later be criticized for anti-Appalachian bias and downplaying western reformers such as
Philip Doddridge." After his 1840 marriage, except for short period in Norfolk, as well as travels within Virginia to deliver historical talks, Grigsby remained at Edgehill the rest of his life, operating the plantation using enslaved labor until the American Civil War, as well as modernizing its agricultural methods. A decade later, on the eve of the Civil War, Grigsby owned 71 enslaved people in Charlotte County, and an additional three in Norfolk (23-year-old Black man and woman and a 14-year-old Black girl). Grigsby delivered the first on his historical lectures in 1848 at the Richmond Atheneum, concerning the
Mecklenburg Declaration of Independence and in 1853 he returned to the state capitol to address the Virginia Historical Society about the Virginia Convention of 1829. Passionate about books and classical art, Grigsby eventually acquired over 6,000 volumes, augmenting his collection with volumes purchased from the library of
John Randolph of Roanoke, who was one of his fellow delegates in the Virginia Convention of 1829–30. Grigsby also supported Virginia sculptor Alexander Galt, and owned his "Columbus", "Sappho", "Psyche", and "Bacchante". His last major prewar address concerned
Littleton W. Tazewell, delivered before the Norfolk bar on June 29, 1860. ==Career at the College==