Spears, 22, wore a Liancarlo gown and her 4-year-old daughter Maddie from a previous relationship served as flower girl. Her sister Britney Spears' two sons, Jayden James and Sean Preston, acted as ring bearers and her father Jamie walked the aspiring singer down the aisle.
Approximately 150 to 200 guests were present at the ceremony, which was held at the Audubon Tea Room.
Spears and Watson have been together for four years and announced their engagement last March. She was previously engaged to Casey Aldridge, the father of Maddie.