Introduction: Tobacco smoking causes various chronic diseases and adds costs to healthcare systems. The current smoking cessation interventions mostly target smokers who are ready to quit and are reactive in recruitment. Recently, mobile phones have become a new tool for promoting smoking cessation. The aim of this paper is to present a study protocol on a quasi-experimental study investigating the effects of a workplace mHealth intervention for smoking behaviour. Methods: A quasi-experimental study will be conducted among employees in an academic institution in Malaysia. The intervention group will receive a theory based WhaSTOP module via WhatsApp and will be compared with the control group (receive usual care). The primary outcomes are stage movement and the number of cigarettes per day. The secondary outcomes include knowledge of smoking, quit attempt, nicotine dependence, 7-day point prevalence of smoking abstinence, and the Transtheoretical Model constructs. A generalised estimating equation analysis will be performed to determine the effects of the intervention. Discussion: This protocol will provide a novel method to proactively approach smokers regardless of readiness to quit and to guide them through the stages of change so that they will be ready to take action to quit. This research will also provide insight into whether the intervention can be utilised as an additional tool for smokers at the workplace to quit smoking. Trial Registration: The trial was registered with the Iranian Registry of Clinical Trials (Registry Number IRCT20220415054539N1).