To uncover perspectives and refine 12 initial program theories concerning the implementation of pain management interventions in intensive care units. Contexts enabling implementation are delineated, and causal mechanisms within these contexts are described. A realist evaluation approach was employed. Fourteen purposively selected Australian nurses of variant roles were virtually and individually interviewed between July and September 2023. Participants were presented with initial program theory, and their perspectives were collated. Data were analysed using an integrated approach of context (C), mechanism (M), outcome (O) categorisation coding, CMO configurations connecting and pattern matching. Pain management interventions work if perceived to be beneficial, precise, comprehensive and fit for purpose. Nurses should be willing to change attitudes and update knowledge. Unit leaders should nurture the development of nurses' professional identity, access to learning, autonomy and self-determination. Organisations should change the infrastructure, provide resources, mitigate barriers, develop shared mental models, update evidence and institute quality assurance. Adherence to interventions is affected by the outcomes of implementation and intrinsic merits of interventions. In these contexts, confidence is boosted; feelings of empowerment, self-efficacy, reflective motivation, trust, awareness and autonomy are developed; and capacity is built. Furthermore, frustration from the variability of practices is reduced, accountability and ownership are augmented, yielding positive implementation outcomes. Findings have implications on nurses, team leaders and organisations concerned with implementation. The findings provided a fortified understanding of conditions favouring successful implementation of pain management interventions. Actions should be undertaken at an individual, unit and organisation level to ensure successful implementation. RAMESES II Reporting Standards for Realist Evaluations informed presentation of study. Intensive care nurses contributed insights to refine the program theory.