His grandfather, Dr. D.W. Roberts, was an early Republican, including a delegate to the 1860 Republican National Convention which nominated Abraham Lincoln for President in 1860, but Marmaduke Dent would be a lifelong Democrat and Populist.
Despite his young age, Marmaduke Dent volunteered for the 6th West Virginia Cavalry during the American Civil War.
After the war, he enrolled in the first class of the new West Virginia University, and in 1870 became the first graduate (B.A.)
Dent worked as a teacher after graduation, as well as read law and was admitted to the bar in 1875, in Grafton, West Virginia, where he lived the rest of his life.
In 1898, he wrote the opinion in Carrie Williams v. Board of Education which ruled that black students were entitled to the same length of school term as white students and that teacher Williams was entitled to the same pay.