Research has consistently found that gratitude predicts life satisfaction. Unfortunately, only a few underlying psychological processes (e.g., mediators) have been tested, using only cross-sectional designs. Nonetheless, novel methodological research argues that mediations should be tested using only longitudinal or experimental data. Thus, we extended current research into the gratitude-life satisfaction link by testing, longitudinally, two unexplored mediators: the satisfaction (BPNS) and frustration (BNPF) of the three basic psychological needs for autonomy, competence and relatedness as proposed by Self-determination theory (SDT). A three-wave longitudinal design among a representative sample of Chilean adults found support for our hypothesis: Gratitude at T1 predicts higher BPNS and lower BPNF at T2, which in turns predicts higher life satisfaction at T3. Key theoretical and practical implications for gratitude and SDT research are discussed.