Engaging non-experts in matters of science and technology has been increasingly stressed in both rhetoric and action during the past decades. Under the call for moving participation upstream, agenda setting processes have been identified as viable entry point for laypeople’s experiential and value-based knowledge into science, technology and innovation governance (STI). Harnessing visioning for target setting promises to elicit such knowledge, whilst at the same time evading the dilemma of informing participants about STI that does not exist prior to engagement. To test such claims, we investigate a large-scale citizen-visioning exercise employed as an initiation of a transdisciplinary research and innovation agenda setting process, namely CIMULACT. In a comparable Europe-wide process, more than 1000 laypeople (citizens) produced 179 visions of desirable futures which built the basis for co-creating future research topics for advising the EU research and innovation programme Horizon 2020. We provide in depth insights into the visioning methodology for inclusion of citizens into STI agenda setting, and discuss room for methodological improvement regarding potential loss and gains of creativity and diversity of opinions considering empirical results of ex-post participant evaluation questionnaires (n ≈ 964). The discussed data shows a generally positive evaluation of the process and engagement, since citizens are in retrospective content with the process and visions, they would participate again in a similar event, and they are in favour of the EU to continue hosting such events in the future. However, citizens were rather sceptic whether the results actually (can/will) have an impact on the stated aim of integration in research and innovation agenda setting.