Unfortunately, it is unknown how Russian Zoomers form their purchase intentions towards co-branded products. The research goal was to advance a comprehensive framework of marketing stimuli that facilitate purchase intention of Russian consumers of Generation Z. Stimulus–Organism–Response paradigm and Theory of Planned Behaviour were integrated in the theoretical framework. 200 Russian representatives of Generation Z participated in a study based on hypothetical scenarios of collaborations between local Russian brands. Structural Equation Modelling and Confirmatory Factor Analysis were conducted. The results show that the influence of country-of-origin factor, cause-related nature of initiative and celebrity endorsement on purchase intention towards co-branded products is mediated by attitude and subjective norms within the organism stage of cognitive information processing. Meanwhile, the mediating role of perceived behavioural control was not statistically significant. If Zoomers perceive the design or social relevance of a co-branded product positively, they are likely to purchase the product. The study provides a theoretical contribution by integrating Stimulus–Organism–Response paradigm and Theory of Planned Behaviour to explore the relevance of co-branding initiatives for business-to-customers brands. Also, the research emphasizes a new perspective of the country-of-origin factor in co-branding studies. The study provides guidance for marketing and branding managers developing co-branding initiatives for Zoomers.