Background: This study was the final phase of a participatory design (PD) project aimed at developing professionally led online art therapy groups for young adults with cancer. Methods: We invited seven professionals with a range of relevant expertise to take part in a PD process that emphasized hands-on creative interaction. Each participant experienced one or more online art therapy sessions and provided feedback that we analyzed with qualitative thematic analysis. Results: The analysis yielded six inter-related themes representing three types of experience (comfort, sense of connectedness and expression) and three types of therapeutic action that supported these experiences (facilitation, group support and dialog about the art). Conclusions: The results assured us that our newly developed mode of psychosocial support was ready for online delivery to young adults with cancer. The results provided insight into therapeutic processes in online art therapy groups, especially with regard to collective meaning-making and sense of connection.