
McCallum's father, John Neil McCallum Sr., was a theatre owner and entrepreneur, who built and for many years ran the 2,000 seat Cremorne Theatre on the banks of the Brisbane River. After emigrating from Scotland, McCallum Snr. became an accomplished musician, and was soon heavily involved in Brisbane's entertainment scene. His mother was an accomplished amateur actress who was born in England.
In 1918, McCallum Jr. was born in Brisbane during the opening night of a comedy performance. After his birth, a family friend sent his father a wire: 'Congratulations on two howling successes'.
McCallum was exposed to acting at a young age: his early childhood was full of backstage encounters at the Cremorne with the wide variety of performers who frequented his father's theatre. Although McCallum and his two younger brothers received their primary school education in the UK, the family returned to Australia once the Great Depression started. His secondary education was at the Anglican Church Grammar School in Brisbane.
His early theatrical training was with Barbara Sisely at the Brisbane Repertory Company.

Forever Ealing
2002 · as Self

The Magic Box
1952 · as Sitter in Bath Studio

Smiley
1956 · as Jim Rankin

The Long Memory
1953 · as Supt. Bob Lowther

The Calendar
1948 · as Capt. Garry Anson

The Woman in Question
1950 · as Michael Murray

Lady Godiva Rides Again
1951 · as Larry Burns

Bush Christmas
1947 · as Narrator (voice)

It Always Rains on Sunday
1947 · as Tommy Swann

Port of Escape
1956 · as Mitch Gillis

Derby Day
1952 · as Tommy Dillon

Melba
1953 · as Charles Armstrong

Trent's Last Case
1952 · as John Marlowe

A Boy, a Girl and a Bike
1949 · as David Howarth

Miranda
1948 · as Nigel

The Loves of Joanna Godden
1947 · as Arthur Alce

Trouble in the Glen
1954 · as Malcolm

Traveller's Joy
1950 · as Reggie Pelham