William Baillie of Polkemmet, descended from an old Linlithgowshire family, was educated for the bar and became an advocate in 1758. He served for over twenty years as Sheriff-Depute before being appointed to the bench in 1792, where he was known for his good nature, practical judgment, and occasional use of broad Scots rather than technical legal reasoning. Though not regarded as a leading legal scholar, his sound sense suited him well to judicial duties, and he remained active until shortly before his death. Twice married, he left a surviving family from his first marriage, while a baronetcy intended for him was later granted to his son. A tall and handsome man, he was also a strong supporter of the Church and warmly hospitable to the clergy.