Background: Postpartum haemorrhage (PPH) causes a significant burden worldwide, as a leading cause of maternal deaths. Strategies to reduce PPH mortality and morbidity include improving health services and biomedical interventions. For success these strategies require patient uptake. Supporting uptake is challenging, due to in part to mechanistic approaches explaining behaviour and the absence of details explaining interactions. This research aims to improve understanding of treatment seeking behaviour for postpartum haemorrhage with the creation of a de novo process stage model informed by complexity theory using the example country of Nigeria. The model portrays complexity by considering “all” influencing elements, interactions between elements within and across stages, and interaction uncertainty and variation on collective element effects. Methods: Structure and inputs were informed by a systematic literature review and by key informants. The model includes six stages, where women can move through the process of care seeking, and move forward, loop back, or exit the model based on collective interaction effect, which is described in detail. Additionally, an example of practical model use is provided, that estimates system changes to access and availability elements, which demonstrates the interconnectedness of elements in the system and the need for holistic change. Further developments of the model are also presented: logic expressions representing interactions and effects by stage, and a model tree that expresses variation. Results: The model demonstrates a potentially important venture into using complex systems theory to describe behaviour, by demonstrating the existence and importance of interactions, proposing how numerous collective interactions occur, and with considerations of uncertainty and variation. Evidence to inform the model also highlights the importance of the multi-directional effect of elements, thereby contesting approaches that address elements as singular units. The model also provides through an evidenced informed approach, new identification and insight into the key stages of the care seeking process, which includes the pivotal role of beliefs and judgments. Conclusion: These findings and results can help to improve how treatment seeking behaviour for postpartum haemorrhage is understood and thereby inform more effective policy to reduce mortality and morbidity.