Before entering politics, Jennings was a farmer.Jennings was active in New Zealand Federated Farmers, becoming its National President in 1990. He served three years. Prior to this he was National Dairy Section Chairman. He was a director of the Karamea Dairy Company, Atas Marketing Meat Ltd and Combined Rural Traders Ltd. He also helped start the Queen Elizabeth II National Trust and was a director for nine years. Jennings was active in PBEC and attended a number of trade talks on behalf of farmers.
Jennings was involved in an international charity, Bright Hope World, based in Christchurch, New Zealand. He is now a director of several companies involved in exporting food and beverages in New Zealand.
Clayton, Christopher; Askwith, John E. (eds.) (1991), Agricultural innovation, how to make a difference now: a conference to identify opportunities for New Zealand agriculture, Friday and Saturday 5 & 6 April 1991, MAF Flock House, Bulls: conference proceedings, Wellington, [N.Z.]: Ministry of Agriculture and Fisheries, ISBN0-477-08152-5
Jennings' contribution is a co-authored paper (with Rodger Slater) entitled: "Innovation on-farm."
ACT Members of Parliament. (2001), Closing the gaps: policy papers, Wellington, [N.Z.]: ACT New Zealand Parliamentary Office, ISBN0-9582178-1-5
Jennings' contribution is a paper entitled: "Local government."
Old values, new ideas, Wellington, [N.Z.]: ACT New Zealand Parliamentary Office, 2002
Jennings' contribution is a paper entitled: "Our rural future."
Question of privilege referred 21 July 1998 concerning Buchanan v Jennings : report of the Privileges Committee, Wellington, [N.Z.]: Published under the authority of the House of Representatives, 2005