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Objective To identify active ingredients of smoking cessation interventions for (expectant) parents experiencing socioeconomic disadvantage.Data sources Systematic search of 11 electronic databases from 1990 up to 6 May 2025. Reference lists and citation records of relevant reviews and included studies were also screened.Study selection Qualitative, quantitative and mixed-methods studies reporting on smoking cessation interventions and their effectiveness among (expectant) parents experiencing socioeconomic disadvantage were eligible.Data extraction We extracted data on study characteristics, methodological quality (Mixed Methods Appraisal Tool), intervention content (behaviour change technique (BCT) taxonomy v1), delivery (Template for Intervention Description and Replication) and outcomes related to effectiveness, reach and retention.Data synthesis Out of 1727 screened records, 62 interventions from 63 articles met inclusion criteria. Effective interventions applied a broader set of BCTs (M=8) than ineffective ones (M=5), particularly from BCT groups, ‘goals and planning’, ‘shaping knowledge’, ‘reward and threat’, ‘feedback and monitoring’ and ‘social support’. Increased intensity and duration of the intervention were also associated with higher effectiveness. Qualitative data indicated that low burden, flexible and relational delivery (eg, empathetic and culturally sensitive) supported reach and retention. Implementation success was shaped not only by content but also by accessibility, contextual fit and proactive engagement strategies.Conclusions Effective interventions for (expectant) parents experiencing socioeconomic disadvantage combine a broad set of BCTs (particularly goals, planning, instruction, rewarding, monitoring, feedback and social support) with delivery that is accessible, personalised and relational. These strategies enhance recruitment, retention and effectiveness, providing concrete guidance for designing more equitable cessation support.PROSPERO registration number CRD42023452795.