Self-Determination Theory (SDT) has consistently shown that the satisfaction of the basic psychological needs for autonomy, competence and relatedness are essential nutrients for optimal human functioning across a diverse range of domains such as family, sports, education and work. SDT has also found that materialism—the relative importance attached to extrinsic versus intrinsic life goals—not only reduces need satisfaction, but also increases need frustration. Yet, what psychological mechanisms explain this association remain unknown. We theorized that dispositional gratitude might play a role. Thus, we tested the longitudinal mediational effects of gratitude in the link between materialism and need satisfaction/frustration, using a three-wave longitudinal design over six months among a large sample of Chilean adults (N = 1841). Importantly, we used the two most established materialism scales: the Aspiration Index (AI) and the Material Values Scale (MVS). Results showed consistently (using either the AI or the MVS) that higher materialism at Time 1 prospectively predicts lower gratitude at Time 2, which in turn prospectively predicts lower need satisfaction and higher need frustration at Time 3. Our results extend SDT and gratitude research in important ways. First, we found a theoretically sound mechanism that accounts for the materialism—basic psychological needs link. Second, expanding on previous research, we found that (a) materialism increases need frustration over time directly, but also through the mediation of gratitude; (b) gratitude decreases need frustration. Theoretical and practical implications are discussed.