Robert Watson Sadler was born in Charlottesville on October 19, 1899, the son of William Robert and Mary Ann Hall Sadler. Watson served in World War I, attended Randolph-Macon College and earned a law degree from the University of Virginia in 1923. When Long's partner left law practice to become Charlottesville's postmaster, he took Watson Sadler as his partner. For the next 25 years Long and Sadler practiced together, although Sadler handled most of the cases since Long was occupied as Commissioner of Accounts. During the last two years of the partnership, Sadler was also justice of the peace, and civil and police justice for Charlottesville. In 1951 he was appointed Corporation Court judge, a position he held until a cerebral hemorrhage caused his sudden death in 1957. From the time Sadler became judge Long practiced alone, although for a number of years prior to his death he shared office space with his friend Henry B. Goodloe. Toward the end of his life he employed office assistants, first, Anne Irving Cox and later, Emily Y. Wilson. 

Sadler's memberships included the Lions' Club, Elks' Lodge, American Legion, Young Men's Business Club, and Red Land Club.

Watson Sadler was married to Elizabeth Randolph Dey, and their children were Mrs. John L. Sadler [?], Diane Randolph Sadler, and Robert Watson Sadler, Jr. Watson Sadler died on June 23, 1957 at the age of 57.