Poly(l-glutamic acid)-b-poly(Nγ-acetyl-l-2,4-diaminobutyric acid), P(Glu-b-NADA), amphiphilic block-co-polypeptides with different hydrophobic/hydrophilic ratios were synthesized as drug carriers for dermal delivery. The block-co-polypeptides were prepared using ring-opening polymerization (ROP) of γ-benzyl l-glutamate N-carboxyanhydride and polycondensation of the activated urethane derivative of Nγ-acetyl-l-2,4-diaminobutyric acid. Structures and conjugations of two blocks were successfully confirmed by 1H NMR, FTIR, DOSY NMR, GPC, and TGA. The nanocarriers were loaded with 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (m-THPP), a close congener of the approved photosensitizer 5,10,15,20-tetrakis(3-hydroxyphenyl)chlorin (m-THPC, temoporfin), and the loading capacity was found to be dependent on the composition of the block-co-polypeptides. Among the synthesized polymers, P(Glu55-b-NADA20) with moderate hydrophobic content showed the highest drug loading capacity of 4 wt % and self-aggregated into spherical nanoparticles with a size of 180–200 nm, which was confirmed by TEM and DLS. In an in vitro drug release study, P(Glu55-b-NADA20) could release m-THPP in a controllable manner. Furthermore, the synthesized polymer P(Glu55-b-NADA20) did not show high toxicity against HaCaT and HeLa cells up to 1000 and 500 μg mL–1, respectively, in an in vitro cell viability assay. Finally, it was shown in an ex vivo skin penetration study that the ionic amphiphilic block co-polypeptide enhanced the m-THPP penetration into human skin compared to base cream up to a factor of 12. m-THPP was released from P(Glu55-b-NADA20) to the viable epidermis while the polymer was deposited in the skin’s stratum corneum. Taking advantage of its excellent biodegradability, the low cytotoxcity, and efficient skin penetration, the synthesized block-co-polypeptide has the potential for future topical delivery systems.