 Whilst still at college, Pennington began working in the family retail feed and seed store founded in Madison, Georgia in 1945 on Main Street by his father, Brooks Pennington Sr. Over the course of 50 years, he built a warehouse and developed the wholesale side of the business and also developed new agricultural crop varieties, seed coatings and seed treatments.He retired as President and Chairman of Pennington Seed Inc. due to ill health in the mid-1990s., the annual turn-over had grown to over $200 million.Pennington was also served as president of the Georgia Seedsmen's Association, the Southern Seedsmen's Association, and the Southern Field Seed Council.