Background In the absence of a cure or effective treatment for dementia, attention has shifted towards identifying risk factors for prevention. Subjective Cognitive Decline (SCD) describes self-perceived worsening of cognition despite unimpaired performance on neuropsychological tests. SCD has been associated with an increased dementia risk and steeper memory decline. Repetitive negative thinking (RNT) is a transdiagnostic process that manifests across several mental health disorders associated with increased vulnerability to dementia. RNT has thus been proposed as a candidate marker of risk for dementia and, relatedly, could contribute to the manifestation of SCD. We aimed to investigate the relationship between SCD and RNT alongside other theoretically informed psychological risk/protective factors for dementia and cognitive decline. Methods In a cross-sectional online survey, 491 older adults (mean=64.9 years, SD =4.2; 63.1% female) completed measures of RNT, personality (including neuroticism), purpose in life, worry, rumination, and meditation practice. SCD was assessed continuously via self-perceived cognitive function (Neuro-QoL) and categorically via endorsement (yes/no) of memory complaints. Regression models, using a stepwise backwards elimination, were built to assess associations between SCD, demographics, and all risk/protective factors. Results A total of 24.2% of participants reported memory complaints. In the final prediction models, RNT was the only psychological variable associated with lower self-perceived cognitive function and with a higher likelihood of memory complaints. Conclusions This study empirically corroborates the theoretical relationship between SCD and RNT. RNT, whether it be a prodromal symptom or independent risk factor, is a promising construct for future research on SCD and dementia risk.