This work introduces a synthesis of well-defined thermo and pH dual-responsive poly(N-isopropylacrylamide)-b-poly(4-vinylpyridine)grafted silica nanoparticles (SNPs-g-PNIPAM-b-P4VP) via surface-initiated atom transfer radical polymerization (ATRP). ATRP initiators were attached onto the surfaces of silica nanoparticles followed by ATRP of N-isopropylacrylamide (NIPAM). During the surface-initiated ATRP, free sacrificial initiator and halogen exchange were utilized to render the polymerization in a controlled manner. Because of the retention of the polymer chain's end-group functionality, chain extension with 4-vinyl pyridine (4VP) from the obtained PNIPAM-grafted SNPs (SNPs-g-PNIPAM) was successfully conducted. Kinetics of the chain extension was studied in detail, showing the livingness of this reinitiation process. Subsequent quaternization of the outer P4VP block with methyl iodide led to the synthesized hybrid nanoparticles being well dispersed in aqueous solution. This well dispersibility affords the possibility to study the pH- and thermoresponsive behavior of the diblock copolymer chains on the nanoparticle surface.