Background: Diets high in ultra-processed food and beverage products contribute significantly to global mortality and morbidity from non-communicable diseases (NCDs). Effective responses including regulation are needed to address the commercial drivers which promote the consumption of these products, however, attempts to introduce such policies are commonly faced with vigorous industry opposition. Drawing primarily on the Policy Dystopia Model, a conceptual taxonomy of corporate political activity from tobacco industry research, this thesis explores how ultra-processed food industry (UPFI) actors have attempted to block, delay, or weaken dietary public health policies at various levels of governance. Specifically, I address corporate political activity in the following settings: (1) World Health Organization (WHO) policy recommendations for obesity and dietary NCDs, (2) sugar-sweetened beverage taxation in WHO European Region Member States, and (3) unhealthy food and beverage advertising restrictions across Transport for London. Methods: First, to map UPFI political activity in the context of the WHO, I conducted three separate analyses: a framing analysis of 45 industry responses to five recent WHO consultations to explore discursive (argument-based) strategies; a content and verification- oriented cross-documentary analysis of 26 industry responses to four recent WHO consultations to explore how evidence was used; and a qualitative analysis of key informant interviews, literature, and internal industry documents to investigate instrumental (action-based) strategies. Second, a qualitative survey was conducted with key stakeholders in WHO/Europe Member States to collect information on corporate political activity in the context of sugar-sweetened beverage taxation. Third, I explored commercial opposition to the Transport for London advertising restrictions using consultation documents and correspondence obtained via Freedom of Information Act requests. Findings: (1) In the context of the WHO, most formal interactions took place via business associations that organise a range of UPFI actors, rather than individual corporations, owing to the UN agency's policies on private sector engagement. Discursively, industry actors emphasised potential negative effects of regulatory approaches, arguing that the WHO should recommend voluntary or partnership approaches instead. Alongside arguments regarding specific policy approaches, industry groups positioned themselves as legitimate actors in public health policymaking and their participation as a condition for 'good governance' in line with the Sustainable Development Goals. Although factual claims on NCD policies were made in 18 of 26 industry consultation responses, only ten referenced any evidence, the majority of which was not independent and peer-reviewed. Moreover, we identified three main instrumental strategies used by UPFI actors in attempts to shape WHO policy recommendations: coalition management, involvement in policy formulation, and information management. Alongside working through business associations, coalition management includes more covert science- and policy-focused intermediaries, hiring former WHO staff, and co-opting civil society organisations. Industry involvement in policy formulation manifested largely as efforts to gain Member State support for industry positions, and participation in formal consultations. Information management involves the financing and dissemination of research favourable to commercial interests, alongside the undermining of unfavourable evidence. (2) In all WHO European Region Member States which had implemented a sugar-sweetened beverage tax or attempted to do so, key informants reported industry pushback, which tended to shift from outright opposition to attempts to weaken the policy by raising tax thresholds or exempting certain products. Opposition most commonly manifested in the form of direct lobbying and anti-tax campaigns, with the most prominent arguments focusing on potential negative economic impacts. (3) The Transport for London advertising restrictions were subject to strong opposition by food and advertising industry actors who - directly and via third parties - had significant access to the policy process and officials. Discursively, opposition primarily manifested in claims that the policy would fail to have the intended public health impact and cause economic harms. Conclusions: UPFI political activity resembles that of the tobacco industry, suggesting that increased coherence in the way we govern interactions with these actors may be appropriate. I further propose that by encouraging a largely uncritical approach to collaboration with the private sector, the ideal of multistakeholder governance may undermine urgently needed efforts to address dietary NCDs.