Cowpea (Vigna unguiculata L. Walp) is a vital pulse crop cultivated in sub-Saharan Africa, Asia, and the Americas, offering numerous agricultural, environmental, and economic benefits to smallholder farmers. Particularly significant in West Africa, cowpea holds potential for enhancing nutrition and alleviating rural poverty. Being rich in protein, carbohydrates, essential amino acids, and antioxidants, cowpea seeds serve as a nutritious food source, but it has very low oil content. To enhance its nutritional value, we introduced a gene cassette containing three oil-related genes (oleosin, WRI1, and DGAT1) to increase oil content in cowpea seeds. While successful in other crops, this approach had not been tested in legumes before. Our study yielded three transgenic lines with approximately sevenfold higher oil content compared to non-transgenic controls. However, this increase came at the expense of reduced grain size and yield, as well as diminished protein and starch levels but elevated soluble sugar concentration. In exploring the effects of increased oil content on other metabolic pathways, we conducted transcriptomic RNAseq analyses at four seed development stages on a high-oil transgenic line and control. This analysis identified potential target genes to guide future attempts aimed at further enhancing oil content in cowpeas and other pulses while preserving seed composition.