Over the past few years, the organometalled compounds, including ruthenium, gained a lot of attention as anticancer agents. We report on the clioquinol–ruthenium complex [Ru(η⁶-p-cymene)(Cq)Cl] as a potent inhibitor of cathepsin B, a lysosomal cysteine peptidase, involved in tumour cell invasion and metastasis. In the low micromolar concentration range, the clioquinol–ruthenium complex did not exhibit cytotoxic effects on MCF-10A neoT and U-87 MG cells; it did, however, significantly reduce their ability for extracellular matrix degradation and invasiveness in two independent cell-based models, measuring either electrical impedance in real time or the growth of multicellular tumour spheroids implanted in Matrigel, a model representing the extracellular matrix. These results establish ruthenium based organometallic compounds as promising candidates for further pre-clinical studies as anticancer therapeutics.