Jonathan was born in 1926. He was a medical practitioner like his father.
He married in 1952 in Paddington to Helen Hope Whistler Street. Helen was born in 1928.
They had 4 children:
- Katherine Anne Halliday
- Michael Andrew Halliday
- Susan Jane Halliday
- Christopher John Halliday

Helen died on 04/08/1999 in St Luke’s Hospital in Potts Point, Sydney.
Jonathan died on 07/07/2011.