Evidence-based public health requires research to support policy. There is a large amount of literature on strategies for knowledge translation or more discursive knowledge exchange. However, little evidence exists for their effectiveness and underlying mechanisms, especially with regard to multisectoral, multidisciplinary evidence in knowledge mobilisation. Taking the opportunity of a knowledge exchange forum at the end of a natural experimental study, we investigated how stakeholders assess, negotiate, and use multisectoral evidence. Participants represented both existing and newly interested stakeholders of the natural experimental study, from national and local government, the third sector, and academia. We conducted participant observation during an interactive event with 41 stakeholders and semi-structured interviews with 17 of them. Formal and informal interactions between stakeholders were recorded in field notes. Interviews considered the event format and content as well as knowledge exchange in general. Thematic content analysis of field notes and transcripts was undertaken. Stakeholders working across sectors expressed uncertainties about finding a common language between research and practice and between sectors, and about who had the capacity to translate across these boundaries. They also expressed differing expectations of evidence. Whereas public health specialists tended to have a hierarchical view of evidence that favoured trials, transport specialists tended to prefer case studies as precedents for workable solutions. However, stakeholders encountered uncertainties about their preferred evidence. Population health studies generated more complex results than did those of apparently clear-cut randomised controlled trials; case studies highlighted the context-dependency of evidence and difficulties in transferring insights across settings. Finally, stakeholders had to reconcile uncertainties about “health in all remits”. Despite its premise, public health was not always acknowledged to contribute to the goals of other policy sectors, and stakeholders had to negotiate competing priorities, such as those between health improvement and economic growth, or between integrated and designated budgets. This case study of stakeholders' experiences indicates that multisectoral research, practice, and policymaking require the ability and capacity to locate, understand, and communicate complex evidence from a variety of disciplines, and integrate different types of evidence into clear business cases. Funded by the National Institute for Health Research (NIHR) Public Health Research Programme (project number 09/3001/06) as part of the Commuting and Health in Cambridge study; and initially funded by the Centre for Diet and Activity Research, a UKCRC Public Health Research Centre of Excellence, with funding from the British Heart Foundation, Economic and Social Research Council, Medical Research Council (MRC), NIHR, and the Wellcome Trust, under the auspices of the UK Clinical Research Collaboration. DO is supported by the MRC (MC_UU_12015/6). The funders had no role in study design, data collection and analysis, the decision to publish, or the preparation of the abstract.