Mr Armstrong was born in Coventry on 7 March 1924, son of David Baxter Armstrong, Social Service Officer, and Jean McBride. He was educated at Glencairn Public School, Motherwell, and Dalziel High School, Motherwell.

From 1941 till 1943 Mr Armstrong studied in the Faculty of Arts at Glasgow University, and from 1943 until 1946 he served as a member of the British Section of the Palestine Police Force. While in Palestine he was mainly employed in Criminal Investigation and for a time was British Police Prosecution Officer of Jerusalem District.In 1946 he returned to his studies at Edinburgh University, and he graduated M.A. in 1947. His theological studies were carried out at New College, Edinburgh University, and he graduated B.D. in 1950.

During the period 1949 – 1950 Mr Armstrong was Student Assistant Minister at St. Matthew’s Parish Church, Edinburgh. From 1950 – 1951 he taught at the West School, Lochgelly.

On 21 April 1950 he was licensed by the Presbytery of Edinburgh, and was ordained and inducted on 21 March 1951 to the Parish Church of Rothes (later Rothes-on-Spey). There he remained until 9 February 1955 when he was inducted to Renfrew Trinity Church.

On 16 March 1960 he Married Hazle Kerr, L.R.A.M. and they have one daughter, Morag Kerr.

Mr Armstrong informed the elders on Thursday 24th March 1966 that, after eleven years at Trinity, he had accepted an invitation to preach on 14th April as sole nominee at St. Marnock, Kilmarnock. He was called to the charge and was inducted on Wednesday 15th June 1966.