Modern agriculture seeks, through technology, to increase agricultural productivity, aiming at greater sustainability during food production. The application of vitamins meets this objective, acting as a biostimulant for different cultivation conditions. In this sense, the aim of this research is to evaluate the effect of the foliar application of nicotinamide on the soybean crop in two growing environments. The treatments were composed of the nicotinamide concentrations of 0, 100, 200, 300, 400, 500, and 600 mg L−1 of water applied when the plants were at the R3 stage (beginning of pod formation), exogenously, by foliar spraying. The application of nicotinamide resulted in increases in the vegetative traits of plant height and the number of branches per plant by 9.7 and 7.8%, respectively. Regarding the productive characteristics, considering the average of the two cultivation sites, the application of the vitamin resulted in increments of about 15.62, 18.57, 20.53, 4.32, and 19.19% on the number of pods, number of grains, mass of grains per plant, mass of 1,000 grains, and yield, respectively. In this way, we conclude that nicotinamide, applied at concentrations ranging from 237.8 to 373.8 mg L−1, promotes benefits to soybean growth and yield in different environments, and can be considered as a biostimulant.