In 2009 he was elected by the General Assembly of the United Nations to the United Nations Appeals Tribunal. He was the only American on the sevenmember court. He left the UN court in 2012. 

A Cincinnati native, Painter attended the University of Cincinnati, where he was elected Student Body President in 1969. He earned a BA in 1970 and a JD in 1973. He practiced law for nine years before becoming a judge. 

Judge Painter is recognized as an outstanding legal scholar. More than 400 of Judge Painter's decisions were published nationally, making him one of the most-published judges ever. His opinions have been cited as precedent more than 3,500 times in legal encyclopedias, treatises, law reviews, and other cases. One of his opinions was named one of the six best in the nation for 2005. 

For 20 years (18 editions), Painter was the author of Ohio Driving Under the Influence Law, the only textbook on DUI in Ohio. He is coauthor of another legal treatise, Ohio Appellate Practice. He has written four law review articles, 135 articles for other journals, Internet biographies of Oliver Wendell Holmes Jr., William Howard Taft, and Warren Harding, and a biography, William Howard Taft: President and Chief Justice. Write Well: 25 Rules to Improve Your Business and Professional Writing was published in 2007. 

His book on plain writing, The Legal Writer: 30 Rules for the Art of Legal Writing, was published in 2002, and sold out within a year. The Legal Writer: 40 Rules for the Art of Legal Writing was published in 2003, with a third edition in 2005, and a fourth in 2009. 

As an Adjunct Professor of Law at the U.C. College of Law since 1990, Painter taught agency and partnership for 13 years and now teaches advanced legal writing. He was named Chesley Distinguished Visiting Professor at UC for 2008. He has lectured at more than 250 seminars for the Ohio Judicial College, the Ohio State Bar Association, Professional Education Systems Institute, the National Institute for Trial Advocacy, and countless firms and bar associations nationwide. In 2008, he traveled to Malaysia as one of four international experts on plain-language legal writing. In 2010, he spoke at the Fifth International Conference on Administrative Justice in Montreal. 

Painter has served as a Trustee of the Cincinnati Freestore/Foodbank, the Cincinnati Shakespeare Company, the Cincinnati Bar Association, the American Society of Legal Writers (Scribes), the Mary Jo Brueggeman Scholarship Fund, the Friends of the William Howard Taft Birthplace, and the Citizens School Committee. He is a Master of the Bench Emeritus of the Potter Stewart Inn of Court, an advisor to The Green Bag Reader, and served as a member of the Ohio Supreme Court Board of Commissioners on Grievances and Discipline. He is a member of the Cincinnati, American, and Ohio State Bar Associations, the Plain Language International Network (Plain), Clarity, the National Space Society, the Ohio Historical Society, and the World Future Society.