Dorsey B. Thomas began his career practicing law and operating a tanning business in Haywood County, Tennessee. He transitioned into politics as a member of the Know-Nothing Party and later served as a Unionist during the Civil War era. Post-war, he held various positions in the Tennessee General Assembly and Senate, including serving as speaker of the Senate. Thomas also participated in national politics as a presidential elector. His family had a notable legacy in Tennessee politics, with several relatives holding significant state positions.

Dorsey B. Thomas's political career reveals a strategic blend of regionalism and ideological flexibility, as seen in his shifts from Know-Nothing to Unionist affiliations. His legislative actions often juxtapose traditional party lines, suggesting a deeply localized approach to governance. Despite his long tenure in various state offices, Thomas's rhetoric consistently emphasizes community interests over partisan dogma.