Recent research suggests that mindfulness may foster sustainable consumption behavior through the reduction of the so-called attitude–behavior gap, or by weakening material values while increasing subjective well-being. The current controlled longitudinal study tested these propositions by employing a sustainability-adapted mindfulness-based intervention (sMBI) to two different samples (n = 60 university students; n = 71 employees). Although the intervention successfully enhanced mindful experiences in both samples, we found no evidence for neither direct effects on sustainable consumption behavior or related attitudes, nor for the reduction of the attitude–behavior gap. However, the intervention led to greater well-being in the student sample and suggested a decline of materialistic value orientations in both samples. The results blunt previous claims about potential causal effects of mindfulness practice on sustainable consumption behavior. Nevertheless, they indicate that the sMBI affects behavior-distal variables, such as material values and well-being, which in turn could influence consumption behavior in the long run.