Dean John P. Thomas was educated at the Carolina Military Institute where he earned his B.S. degree. He undertook both the private study and the formal study of law at the University of Virginia.
He married Mary Sumter Waites in 1879.
He practiced law in Columbia until 1916, when he joined the law faculty of the University of South Carolina. He became Dean in 1910 and resigned in 1920.
He was a regular attendant of the American Bar Association meetings. He was an effective teacher and advocate of sound legal educational programs; a financier and member of the South Carolina House of Representatives from 1892 until 1902. He authored many books, pamphlets and papers, and he was an admirer and venerator of the great legal rights of the past. At one time, he was President of the Richland T.B. Association and President of the Standard Building and Loan Association.
A man of firmness and determination, he served his University and the cause of legal education with devotion.