Consumers are increasingly taking up activism to modify, or at the very least, penalize a company's contentious behavior. This paper presents a systematic literature review of 404 studies on consumer activism published between 1975 and 2023, applying the extended stimulus‐organism‐response‐outcomes (S‐O‐R‐Om) framework. It investigates the underlying causes and significant outcomes of consumer activism. The results reveal how various factors such as political conditions, human rights violations, environmental degradation, religion, and consumer disregard stimulate internal evaluations of perceptual, physical, emotional, and philosophical activities in people. These evaluations often prompt consumers to respond via boycotts, anti‐brand activism, commodity activism, and even buycotts, all of which have varying consequences for different stakeholders. The findings suggest that consumer activism can serve as a powerful tool for societal change, shaping brand strategies and influencing business practices. These insights underscore the necessity for businesses to align their operations with the evolving values and expectations of their consumer base, emphasizing the critical role of ethics in consumer‐brand relationships. This research contributes to the understanding of modern consumer behavior by providing the Consumer Activism framework, which is based on the S‐O‐R‐Om framework. This comprehensive exploration provides valuable insights into the mechanisms driving consumer activism and its significant implications for brand management and consumer behavior research. The study also identifies key research gaps in existing literature and offers a detailed set of recommendations to guide future research on the evolving dynamics of consumer activism.