In 1907, Johnson entered Wake Forest University Law School where he graduated in two years. He began practicing law in North Wilkesboro and served as solicitor for 12 years riding the circuit on horse, buggy, and train. In 1927 he joined Brooks, Parker and Smith, a prominent law firm in Greensboro where he moved his family. Four months later he was appointed judge of the Middle District of the Federal Courts. He served thirty years and then held partial retirement status until his death in 1970. He moved his family back to Wilkes and held federal court in Wilkesboro in the old Federal Court building and later in the new federal court building which was given his name sake and named the Johnson Jay Hayes Federal Court Building.

His interest in education did not diminish, and he served as a trustee of Wake Forest University for many years and worked diligently for the removal of his Alma Mater to Winston Salem. Judge Hayes took pride in watching it grow from a small regional college to a nationally recognized college.

In 1960 his interest turned to the community college movement as he was ever mindful of the cost and struggle of his own college years. His effort with the state legislature and the citizens of Wilkes County were the moving force that saw the establishment of Wilkes Community College where a building is named in his honor.

Judge Hayes and his wife, Willa Harless Hayes, were staunch Christians and supporters of their church. He taught the Men's Bible Class in the First Baptist Church in Greensboro and in the Wilkesboro Baptist Church, where it was broadcast until his death.