David Johnston began life in a suburb of Philadelphia. His family moved to Arkansas, where he completed high school and began college studies at John Brown University.
In 1956 the family moved to Iowa, where David completed college studies at Iowa State University. During the next three years, he was a secondary-level teacher in the public schools of Waterloo and Des Moines, Iowa. During his third year of teaching, he married Connie, who would be his faithful partner for 51 years, until her death in 2013.
From 1962 to 1968, David did graduate studies. First, it was three years of graduate study in Economics at Purdue University, where he received a Master of Science degree in 1965. Then it was three years of study at Pittsburgh Theological Seminary, where he received a Master of Divinity in
Following seminary, David became Pastor of the Fairmount Presbyterian Church in Franklin Park, northwest of Pittsburgh. He was there for 30 years. In 1982, both David and the Church were transferred to the Associate Reformed Presbyterian Church.
In 1998, Lifeline Community Church was formed from the Fairmount Church, and David became pastor of Lifeline. He formally retired in 2003, but has continued functioning in a pastoral role by advising, mentoring and assisting in Sunday worship.
In May of 2015, David was honored with the Doctor of Divinity by Erskine College, the College and Seminary of the Associate Reformed Presbyterian Church.