Sustainability science has focused predominantly on external/technological solutions to environmental degradation while giving insufficient attention to the role of spiritual well-being for holistic sustainability. While it is important for students to learn about solutions in a time where environmental problems have been identified as prevalent, that alone is not enough. We propose that sustainability may start as a deep individual internal process manifested as a change of values stemming from enhanced spiritual well-being. The current study examined whether a novel sustainability classroom curriculum, including contemplative practices (CPs), increased traits indicative of spiritual development and well-being and happiness, which are theorized to increase sustainable behavior (SB). Students attended a 15-week university course promoting SB through CPs in a space intended to be safe and supportive. Participants were compared to unenrolled peers and completed pre- and post-intervention quantitative measures of (1) happiness, (2) self-compassion, and (3) SB, and qualitative questions investigating spiritual development and well-being. Multivariate and univariate follow-up analyses indicated that course participation increased student self-compassion and happiness, while SB was unaffected. Qualitative reports indicated that CPs led students to develop spiritual traits, a systems’ thinking mentality and an awareness of their interconnectedness. Students, also, assigned greater importance to spiritual well-being as a prerequisite for SB.