The aim of this work was to determine the variance components and genetic and environmental stability of 12 cowpea genotypes at three locations (South-east of Spain: Cartagena, South and North of Portugal: Elvas and Vila Real, respectively) in the Iberian Peninsula in two consecutive years (2015 and 2016). The genotype, the environment and the genotype × environment interaction significantly influenced all the morphological and agronomical parameters evaluated. For both years, the highest yields were observed at Elvas, whereas Cartagena and Vila real were the most suitable places to obtain crop precocity. Cartagena was the place where the filling of the seed was the fastest, probably due to the higher temperatures and radiation. The thermal time model (effective degree-days) could be used to predict the period of cowpea development, therefore predict flowering and pod maturity date. Correlation analysis showed that days to flowering, days to maturity and the seed yield vs protein content exhibited negative correlations. The highest heritability was found for plant height and pod length at Cartagena and for 100-seed weight at Elvas and Vila Real. In conclusion, the variations that exist in the studied accessions could give rise to a breeding program to develop cowpea cultivars with interesting agronomic traits.