[3][4] On 31 August 1963, John Donaldson married his first wife, Henrietta Clark Horne (1942–1997), at Port Seton.

Donaldson's parents, his elder brother Peter and younger sister Roy also emigrated to Tasmania.

[7] Henrietta died on 20 November 1997, and Donaldson later married Susan Elizabeth Horwood (born 1940) on 5 September 2001.

After Edinburgh, Donaldson moved to Australia to work under the direction of mathematician Professor David Elliott at the University of Tasmania, taking a PhD in Mathematics in 1967.

[10] After receiving his doctorate in 1967, Donaldson remained at the University of Tasmania as a lecturer in applied mathematics, becoming Dean of UTAS Faculty of Science until retiring in 2003.