A novel drug carrier with dual triggerable release properties based on keratin graft poly(ethylene glycol) (keratin-g-PEG) copolymers is reported. Keratin-g-PEG copolymers with different graft densities are synthesized through thiol–ene click chemistry. Taking advantage of the amphiphilicity and the thiol groups of the graft copolymer, nanoparticles stabilized with PEG chains and keratin as the core, bearing glutathione (GSH) cleavable cross-links, are fabricated in aqueous solutions. The keratin-g-PEG copolymer nanoparticles can serve as excellent carriers for doxorubicin hydrochloride salt (DOX·HCl) with a highest loading capacity of 18.1% (w/w). The release of the loaded DOX is sensitive to the concentration of GSH, especially at a GSH concentration of cellular level. Trypsin can further trigger the release of the loaded DOX in the nanoparticles. In vitro cellular uptake experiments indicate that DOX released from the DOX-loaded keratin-g-PEG nanoparticles can be internalized into the cells efficiently, and the loaded DOX shows a faster release into the nuclei of the cells under higher GSH concentrations. The carriers have promising applications as drug carriers for intracellular drug delivery for cancer therapy.