Introduction Integrating smoking cessation supports into lung cancer screening can improve abstinence rates. However, healthcare decision-makers need evidence of cost-effectiveness to understand the cost/benefit of adopting this approach. Methods To evaluate the cost-effectiveness of smoking cessation interventions, and service delivery, we used a cohort-based Markov model, adapted from previous National Institute for Health and Care Excellence (NICE) guidelines on smoking cessation. This uses long-term epidemiological data to capture the prevalence of the smoking-related illnesses, updated through targeted literature searches as required from the core NICE model, with costs extracted from publicly recognised UK sources. Results All smoking cessation interventions appeared cost-effective at a threshold of £20 000 per quality-adjusted life year, compared with no intervention or behavioural support alone. Offering immediate smoking cessation as part of lung cancer screening appointments, compared with usual care (onward referral to stop smoking services), was also estimated to be cost-effective with a net monetary benefit of £2198 per person, and a saving of between £34 and £79 per person in reduced workplace absenteeism among working age attendees. Estimated healthcare cost savings were more than four times greater in the most deprived quintile compared with the least deprived, alongside a fivefold increase in quality adjusted life years accrued. Conclusions Smoking cessation interventions within lung cancer screening are cost-effective and should be integrated, so that treatment is initiated during screening visits. This is likely to reduce overall costs to the health service, and wider integrated care systems, improve quality and length of life, and may lessen health inequalities.