Fields was born in Humble, a northern suburb of Houston, to Mr. and Mrs. Jack Fields Sr. He graduated from Humble High School in his hometown in 1970. Fields earned both Bachelor of Arts and Juris Doctor degrees from Baptist-affiliated Baylor University and Baylor Law School in Waco, Texas, in 1974 and 1977, respectively. After being admitted to the Texas bar in 1977, Fields worked as a lawyer in private practice and as a vice president of a family-owned business through 1980.