A nitric oxide (NO) and carbon dioxide (CO2) dual-responsive block copolymer was self-assembled in aqueous solution upon gas stimuli to form nanostructures. Specifically, poly(oligo(ethylene glycol) methyl ether methacrylate)-block-poly(N,N-diethylaminoethyl methacrylate)-block-poly(2-(3-(2-aminophenyl)ureido)ethyl methacrylate) (POEGMA-b-PDEAEMA-b-PAPUEMA) (termed ODA) triblock copolymers, consisting of a CO2-responsive PDEAEMA block and a NO-sensitive PAPUEMA block, were synthesized using sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The ODA triblock copolymer was found to self-assemble at pH 7.4 into three-layer micelles with PAPUEMA inner cores, PDEAEMA outer cores, and hydrophilic POEGMA coronas. Upon CO2 addition, the collapsed PDEAEMA block became protonated, increasing water solubility following the generation of carbonic acid functionality, resulting in the formation of expanded micelles with PAPUEMA cores. Subsequent NO addition selectively transformed the interior PAPUEMA block into more hydrophobic benzotriazole moieties, driving a morphological transition from swollen micelles to nanorods. Importantly, the transformation from spherical nanoparticles to nanorods in this novel copolymer system is highly specific to NO exposure.