Born in Tuscaloosa to Stancil R. Starnes and his wife, a schoolteacher, Starnes grew up in Forest Park. He earned his bachelor of science at the University of Alabama in 1969 and his Juris Doctorate from Samford University's Cumberland School of Law, where he was editor-in-chief of the Cumberland Law Review and graduated summa cum laude in 1972. After graduating he entered professional practice at his father's law firm. He and his father later co-founded the firm of Starnes & Starnes in 1975, where he practiced for the next 30 years. He is a fellow in the American College of Trial Lawyers and has chaired the Alabama Supreme Court's Advisory Committee on Rules of Civil Procedure.
In 2002, Starnes was the first "Lawyer in Residence" at Cumberland, giving lectures on his specialties of civil procedure and medical liability. As a partner in Starnes & Atchison, Starnes defended University of Alabama president Robert Witt when he was sued over his decision to fire football coach Mike Price.
In 2006, Starnes was approached by Jim Gorrie about taking an executive position in corporate planning with Brasfield & Gorrie, and he accepted it as a chance to "re-energize" in a different field. He was lured away eight months later by Derrill Crowe's request that he take over ProAssurance as chief executive. Starnes served as CEO until July 2019. He held the title of executive chairman until resigning from the board of directors in May 2022. He remains chair of the board for Ascension.
Starnes was appointed to the University of Alabama Board of Trustees in 2017, succeeding fellow insurance executive Johnny Johns. He is an active member of the Cathedral Church of the Advent and the Kiwanis Club of Birmingham. Starnes was inducted into the Alabama Academy of Honor in 2018 and the Alabama Business Hall of Fame in 2020.
- Goodman, Sherri C. (July 15, 2007) "Lawyer takes over as head of ProAssurance." The Birmingham News
- DeButts, Jimmy (April 26, 2007) "ProAssurance taps Starnes as new CEO." Birmingham Business Journal
- Patchen, Tyler (April 11, 2022) "W. Stancil Starnes to retire from ProAssurance board." Birmingham Business Journal