Many viruses have the ability to manipulate cellular signalling pathways in order to overcome obstacles which impede viral replication. These pathways often control critical functions, such as apoptosis, cell proliferation and cytoskeletal reorganisation. Some of these same pathways are aberrantly controlled in tumour cells, where they facilitate metastasis and tumour survival. One of the most commonly dysregulated systems, in this context, is the TGF-β signalling cascade. Observations in our lab suggest vaccinia virus (VACV), an oncolytic virus, can exploit elements of this pathway during infection. Specifically, we found via luciferase assay and western blots, that VACV can potently activate the R-Smad transcription factors, Smad2 and Smad3, as well as the common Smad, Smad4. Using qPCR, immunoblot and immunofluorescence assays, we also detected expression of Smad targets at both the transcript and protein level following infection. Furthermore, using CRISPR-Cas9 and siRNA technologies, we have demonstrated a role for the common Smad, Smad4, in a number of aspects of viral infection, including viral replication, virus-induced cell invasion and cell migration. Interestingly, it appears that activation occurs entirely independently of TGF-β receptor phosphorylation in the VACV context. As of yet, no virus is known to stimulate this pathway in the same manner, or lead to phosphorylation of Smad proteins independently of the TGF-β receptor. Understanding how VACV is able to induce this outcome, without TGF-β receptor input, could be critical in understanding dynamics of non-canonical Smad signalling and developing a more targeted oncolytic VACV.