Transnational tobacco companies (TTCs) interfere regularly in policymaking in low- and middle-income countries (LMICs). The WHO Framework Convention for Tobacco Control provides mechanisms and guidance for dealing with TTC interference, but many countries still face ‘how to’ challenges of implementation. For more than two decades, Thailand’s public health community has been developing a system for identifying and counteracting strategies TTCs use to derail, delay and undermine tobacco control policymaking. Consequently, Thailand has already implemented most of the FCTC guidelines for counteracting TTC interference. In this study, our aims are to describe strategies TTCs have used in Thailand to interfere in policymaking, and to examine how the public health community in Thailand has counteracted TTC interference. We analyzed information reported by three groups with a stake in tobacco control policies: Thai tobacco control advocates, TTCs, and international tobacco control experts. To identify TTC viewpoints and strategies, we also extracted information from internal tobacco industry documents. We synthesized these data and identified six core strategies TTCs use to interfere in tobacco control policymaking: (1) doing business with ‘two faces’, (2) seeking to influence people in high places, (3) ‘buying’ advocates in grassroots organizations, (4) putting up a deceptive front, (5) intimidation, and (6) undermining controls on tobacco advertising, promotion and sponsorship. We present three case examples showing where TTCs have employed multiple interference strategies simultaneously, and showing how Thai tobacco control advocates have successfully counteracted those strategies by: (1) conducting vigilant surveillance, (2) excluding tobacco companies from policymaking, (3) restricting tobacco company sales, (4) sustaining pressure, and (5) dedicating resources to the effective enforcement of regulations. Policy implications from this study are that tobacco control advocates in LMICs may be able to develop countermeasures similar to those we identified in Thailand based on FCTC guidelines to limit TTC interference.