New strategies for the synthesis of multifunctional particles that respond to external stimuli and release biologically relevant agents will enable the discovery of new formulations for drug delivery. In this article, we combine two powerful methods: brush-first ring-opening metathesis polymerization and copper-catalyzed azide–alkyne cycloaddition click chemistry, for the synthesis of a novel class of brush-arm star polymers (BASPs) that simultaneously degrade and release the anticancer drug doxorubicin (DOX) in response to 365 nm light. In vitro cell viability studies were performed to study the toxicity of azide- and DOX-loaded BASPs. The former were completely nontoxic. The latter showed minimal toxicity in the absence of light; UV-triggered DOX release led to IC50 values that were similar to that of free DOX.