Leaf senescence can be triggered and promoted by various environmental stressors, developmental cues, and endogenous hormone signals. Several lines of evidence have suggested the involvement of WRKY transcription factors in the regulation of leaf senescence, but the related signaling pathways and physiological mechanisms remain unclear. In the current study, we initially identified Arabidopsis thaliana WRKY DNA binding protein 45 (WRKY45) as a positive regulator of age-triggered leaf senescence. Mutation of WRKY45 resulted in enhanced leaf longevity in age-triggered senescence, whereas overexpression of WRKY45 significantly accelerated age-triggered leaf senescence. Further investigation suggested that expression of senescence-associated genes was significantly reduced in WRKY45 mutants and significantly enhanced in 35S_pro: WRKY45 transgenic plants. Chromatin immunoprecipitation experiments revealed that WRKY45 directly binds to the promoter of several SENESCENCE-ASSOCIATED GENEs, such as SAG12, SAG13, SAG113 and SEN4. In vivo and in vitro experiments suggested that WRKY45 interacts with RGA-LIKE1 (RGL1), a repressor of the gibberellin (GA) signaling pathway. We determined that RGL1 represses the activation ability of WRKY45, thereby attenuating expression of its regulon. Consistent with this finding, RGL1 overexpression significantly enhanced leaf longevity in age-triggered senescence. Taken together, our findings provide evidence that WRKY45 functions as a critical component of the GA-mediated signaling pathway to positively regulate age-triggered leaf senescence.