BACKGROUND: The 2014 European Union (EU) Tobacco Products Directive (TPD) was negotiated in a changed policy context, following adoption of the EU's 'Smart Regulation' agenda, which transnational tobacco companies (TTCs) anticipated would increase their influence on health policy, and the WHO Framework Convention on Tobacco Control (FCTC), which sought to reduce it. This study aims to explore the scale and nature of the TTCs' lobby against the EU TPD and evaluate how these developments have affected their ability to exert influence. METHODS: Analysis of 581 documents obtained through freedom of information requests, 28 leaked Philip Morris International (PMI) documents, 17 TTC documents from the Legacy Library, web content via Google alerts and searches of the EU institutions' websites, plus four stakeholder interviews. RESULTS: The lobby was massive. PMI alone employed over 160 lobbyists. Strategies mainly used third parties. Efforts to 'Push' (amend) or 'Delay' the proposal and block 'extreme policy options' were partially successful, with plain packaging and point of sales display ban removed during the 3-year delay in the Commission. The Smart Regulation mechanism contributed to changes and delays, facilitating meetings between TTC representatives (including ex-Commission employees) and senior Commission staff. Contrary to Article 5.3, these meetings were not disclosed. CONCLUSIONS: During the legislative process, Article 5.3 was not consistently applied by non-health Directorates of the European Commission, while the tools of the Smart Regulation appear to have facilitated TTC access to, and influence on, the 2014 TPD. The use of third parties undermines Article 5.3.