William McWillie graduated from South Carolina College and was admitted to the bar in 1818. He served as an adjutant during the War of 1812 and held various legislative positions in both South Carolina and Mississippi. McWillie also served as a US Representative for Mississippi and as Governor of Mississippi. His career transitions reflect a progression from military service to public sector roles, showcasing a blend of leadership and governance experience.

William McWillie's political career reveals a deeply rooted commitment to regional governance, underscored by his service in both South Carolina and Mississippi legislatures. His personal military experience and the loss of his son in the Confederate Army suggest a complex stance on military issues, possibly blending personal sacrifice with broader regional loyalties. McWillie's political maneuvers, including his gubernatorial win and subsequent snub by his party, hint at an ideologically agile approach, navigating party lines for the sake of regional interests.