Bob was born and raised in Paxton, Illinois. He graduated from the University of Illinois at Urbana-Champaign in 1959 with a B.S. in Commerce and Law. He graduated from the University of Illinois School of Law in 1961. Bob joined his father, Delmar E. Martensen, in the practice of law in Paxton, Illinois upon graduation. He served as City Attorney for the City of Paxton, Illinois from 1969 to 2012. He is licensed to practice in the Federal District Court and the United States Tax Court. Bob resides at Bayles Lake, Loda, Illinois with his wife, Sue.