In spite of the growing integration of computer-mediated collaborative writing and multimodal composition in second language (L2) classrooms, research on collaborative multimodal writing, as an innovative writing pedagogy, is still underway and largely underrepresented particularly in non-English learning contexts. To bridge this research gap, the author of this study implemented a multimodal writing task in which seven French FL learners jointly created digital postcards describing their vacation activities in groups of two or three over the period of eight weeks. The study sought to explore learners’ perceptions of the benefits and challenges of this type of pedagogy and the factors mediating their writing processes. The analyses of a post-task questionnaire survey and semi-structured interviews, triangulated with the finished products, indicated that overall, collaborative multimodal writing was a motivating learning experience. Several themes emerged regarding the perceived benefits (i.e., improvement in their writing skills, genre awareness and semiotic awareness, mutual learning through peer assessment and easy synchronous writing and revising via Google Docs), as well as challenges (i.e., tensions between partners largely due to frustrations over unequal participation, lack of control over the joint text and technical glitches). This paper provides significant implications for collaborative multimodal writing research and pedagogy.