Agricultural systems support societies in various ways but also cause substantial sustainability challenges. Sustainable agricultural practices are key to achieving sustainability targets, yet we lack generalizable knowledge on why farmers apply such practices. Here, we quantified the relationship between farmers’ adoption of sustainable agricultural practices and their underlying motivational factors. Based on a systematic review, we meta-analyzed 14 motivational factors from 225 studies reporting 522 effect sizes, representing 327,778 farmers from 23 European countries. We found (1) substantially stronger positive effects for general attitude, intention and perceived usefulness compared with economic outcomes and environmental awareness, (2) dissonance between intention and actual behavior, and (3) geographic, thematic, and effort-effect bias in literature. Stimulating the adoption of sustainable agricultural practices hence requires reconsidering the currently strong emphasis on economic factors in favor of a wider set of motivational factors, especially by addressing socio-psychological factors via transparency, communication, and training.