Montgomery Spencer was the son of a minister of the Church of England, the grandson of a general in the Indian Army, and the godson of Bishop Montgomery of Tasmania, the Bishop being father of the Commander of the 8th Army, Field Marshal Viscount Montgomery of Alamein. His secondary education was at Wanganui Collegiate School. As a medical student at Knox College and Otago University, he applied himself to his studies, his hospital duties and his sport with quiet zeal.

At the outbreak of World War I, as a medical student, he joined the New Zealand Medical Corps and was at the Gallipoli landing. He was recalled to New Zealand to complete his medical degree, returning to France as RMO to an artillery unit. After 1919 and the Armistice, and following two years of postgraduate study in the United Kingdom, he had qualified FRCSE and completed his MD (NZ). He returned to Hamilton where he practised for six years. In 1927 he travelled once more to study diseases of children in the USA and was awarded a Rockefeller Scholarship in the Children's Hospital at Harvard University. He later extended his studies in England and Europe. Returning to New Zealand he established himself in Wellington, rapidly building up an extensive practice in children's diseases. He was shortly to be appointed senior physician to the children's wards at Wellington Hospital and continued in his role as a paediatric consultant until 1939, and the beginning of World War II.

Holding the rank of colonel, he was at that time officer commanding 2 Field Ambulance, NZMC. He volunteered immediately for overseas service, entering camp in early 1940 and leaving New Zealand as officer commanding 2 NZ General Hospital. His first assignment was to enlarge a converted hospital to take British and Australian casualties from the first Libyan advance and later from the actions in Greece and Crete. In October 1941 his orders were to proceed and establish a tented hospital in the Western Desert, a unit which was later transferred to Nazareth and then to the Canal zone. For his services in these operations he was mentioned in dispatches and was awarded the OBE.

Destiny did not hold her hand for long. He contracted typhus and died at Tripoli in June 1943, within six days of admission to an NZ General Hospital at the untimely age of forty-nine, to the distress of an unusually wide circle of friends. It was thought that he had contracted the infection when sleeping in an old barrack building at Sidi Barrani on his way to Tripoli. He had served in the New Zealand Military Forces from college days until his death.

Recorded tributes of his superiors in the medical services of 2NZEF are worthy of record. Brigadier HS Kenrick, DMS, 2NZEF Middle East said `We had little warning that we were to lose one of the most experienced medical officers and best loved friends' and Brigadier K MacCormick later DMS, 2NZEF CMF said `His record here is one of devoted service. Throughout three years he never ceased to search for and devise improvements for the welfare of those in his charge'. The biographer for the New Zealand Medical Journal said of his chosen field of work in Wellington `To all children he was a companion rather than a mentor'. Finally his own introduction to a still unpublished article, and perhaps an appropriate epitaph says `Life's greatest satisfaction is derived from achievement'.

He left a wife, three daughters and a son who at the time of his father's death was serving with the Royal Navy. His wife was Marjorie Balcombe-Brown from an old Wellington family. After his death, a sum of money was made available by his family and is held in trust by the RACP to provide in perpetuity a memorial oration named the Montgomery Spencer Oration, being held at appropriate intervals on the occasion of annual clinical and scientific meetings and to be given by a distinguished speaker on a suitable topic, related to the health of children.