The article outlines the contours of a new methodology in the study of co-branding, based on M. DeLanda’s theory of assemblages, developed in line with the cutting edge of modern philosophical thought: object-oriented ontology. It is demonstrated that the relevance of its development is linked to the changes in brand alliance practices occurring under the influence of globalisation and digitalisation processes. Transformations characteristic to merging brands, and related to both their rise in number and diversification were proven to be part of a more global tendency towards the complication of social reality, and cannot be explained within the ‘perceived conformity’ paradigm that dominates co-branding. The author’s approach is conceptualised using comparative and discursive analysis methods, the essence of which lies in deconstructing the established notions of brand alliances as internally consistent alliances with an intelligible logic. Real co-branding cases were provided to demonstrate a tendency towards forming alliances evaluated as ‘irrational’, ‘sudden’, and ‘unpredictable’. To bridge the gap between theory and practice, it has been suggested that co-branding should be seen as an assembly process and that alliances themselves should be seen as systems of an assemblage nature. It is stressed that the representation of brands through the lens of the assemblage theory allows us to demonstrate their heterogeneity, plasticity and openness to change and interactions, which contributes to the formation of brand alliances. The conclusion outlines the prospects of applying the author’s approach to the field of co-branding, highlighting that the proposed optics of the theory of assemblage contribute to achieving the necessary flexibility in forming brand alliances relevant to the complexity and diversity of the modern digital era.