Shortly after graduating, Jennings was appointed the first Assistant Manager of the Berri Experimental Orchard on 14 February 1945.

[1] In early 1957, just as the great 1956 Murray River flood was receding, the family moved to Waikerie when Jennings was appointed Horticultural Adviser.

[2] His district covered Nildottie, Swan Reach, Blanchetown, Morgan, Cadell, Ramco, Waikerie, Kingston On Murray and lots of smaller areas in-between.

At various times, Jennings was also Secretary of the SA Avocado Growers Association and the SA Citrus Improvement Committee and was a member of the River Murray Water Resources Advisory Committee, Golden Heights Irrigation Area Board of Management, Loxton/Waikerie Animal Plant Control Board, and the Riverland Community Health Services Inc. John also served as Councillor on the District Council of Waikerie for 12 years representing both Ramco and Town Wards.

John married Judith (Judy) Good (née Hudson) 27 July 1996 Waikerie, South Australia.