In 1969 John McDuff founded Faith Assembly of God in Pasadena, Texas. It became one of the most powerful church in America. McDuff served the Assemblies of God as Assistant District Superintendent of the South Texas District. He was well known as a camp meeting speaker.
McDuff and his siblings were well known as the McDuff Brothers a gospel trio that recorded a number of successful projects.
John continues to serve Faith Assembly as an associate pastor, assisting his son, Pastor John D. McDuff.