He was born in Wisbech, Cambridgeshire on 15 July 1922. Missin's parents lived in a small village, Gorefield just outside Wisbech. He was awarded his FRCO CHM in 1947 and took a Doctor in Theology (Church Music) degree from Geneva Theological College, America. He also held the A.D.C.M. (Archbishop of Canterbury's Diploma in Church Music).
He was married to Muriel, and they had two sons. His ashes are interred in the churchyard at St Paul’s Church, Gorefield, Wisbech.