We conducted a qualitative longitudinal study using a sample of 16 smokers divided into 2 cohorts (one used agamified intervention and the other used a nongamified intervention). Each participant underwent 4 semistructured interviewsover a period of 5 weeks. Semistructured interviews were also conducted with 4 experts in gamification, mHealth, and smokingcessation. Interviews were transcribed verbatim and thematic analysis undertaken.Results indicated perceived behavioral control and intrinsic motivation acted as positive drivers to game engagementand consequently positive health behavior. Importantly, external social influences exerted a negative effect. We identified 3critical factors, whose presence was necessary for game engagement: purpose (explicit purpose known by the user), user alignment(congruency of game and user objectives), and functional utility (a well-designed game). We summarize these findings in aframework to guide the future development of gamified mHealth interventions.Gamification holds the potential for a low-cost, highly effective mHealth solution that may replace or supplementthe behavioral support component found in current smoking cessation programs. The framework reported here has been built onevidence specific to smoking cessation, however it can be adapted to health interventions in other disease categories.