Genetically Modified Herbicide Tolerant (GMHT) maize tolerant to the broad-spectrum herbicide glyphosate is a possible addition to the weed control toolbox of European farmers. We modelled ex-ante the economic and environmental changes associated with the adoption of GMHT maize in Europe. A dataset from a survey of maize farmers conducted in seven European countries was used to construct a baseline of current herbicide use and costs in maize cultivation. A stochastic partial budgeting model was used to simulate the impacts of adoption of GMHT maize on farmers’ gross margin. We built a first scenario representing the initial years of introduction of the technology (low, fixed technology fee and an herbicide program for GMHT maize based exclusively on glyphosate). Assuming that all farmers who benefit from the technology will adopt GMHT maize, the model predicts very high adoption rates for all seven countries (60–98% of maize farmers depending on the country). We also calculated the Environmental Impact Quotient Index (EIQ) associated with herbicide use when switching to GMHT maize. In ES, PT and CZ, countries with a high baseline of herbicide use in maize, the majority of adopting farmers (60–79%) will also experience reductions in EIQ, realising the economic and environmental potential of the technology. In contrast, for countries such as FR, DE and HU, only a fraction (19–28%) of adopting farmers experiences a decreased EIQ. In this situation, a purely economic-driven adoption may result in increased EIQ for many adopting farmers. We also explored the effects of additional scenarios introducing more complex herbicide programmes for delaying weed resistance and changes in the technology fee of GMHT seeds. In these scenarios adoption levels decrease but the technology is still economically attractive for a large share of farmers (14–86%), showing that a sustainable use of the technology to lower the risk of weed resistance development is not in contradiction with its economic attractiveness. These scenarios do not change significantly the proportion of adopting farmers for which the EIQ decreases. The pattern of two groups of countries in terms of potential environmental effects remains and calls for a better identification of the subset of farmers with economic and environmental potential for the technology. Finally, our results confirm that farmers are the main economic beneficiary of GMHT maize introduction while the technology provider is not able to capture all the benefits generated by the technology due to heterogeneity within the farmer population.