Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) nanoparticles, after being coated with polyethylene glycol (PEG), are used as a drug carrier to load various types of aromatic therapeutic molecules, including chemotherapy drugs doxorubicin (DOX) and SN38, as well as a photodynamic agent chlorin e6 (Ce6), through π–π stacking and hydrophobic interaction. Interesting functionalities of PEDOT:PSS-PEG as an unique versatile drug delivery platform are discovered. Firstly, for water-insoluble drugs such as SN38, the loading on PEDOT:PSS-PEG dramatically enhances its water solubility, while maintaining its cytotoxicity to cancer cells. Secondly, the delivery of Ce6 by PEDOT:PSS-PEG is able to remarkably accelerate the cellular uptake of Ce6 molecules, and thus offers improved photodynamic therapeutic efficacy. Using DOX-loaded PEDOT:PSS-PEG as the model system, it is demonstrated that the photothermal effect of PEDOT:PSS-PEG can be utilized to promote the delivery of this chemotherapeutic agent, achieving a combined photothermal- and chemotherapy with an obvious synergistic cancer killing effect. Moreover, it is also shown that multiple types of therapeutic agents could be simultaneously loaded on PEDOT:PSS-PEG nanoparticles and delivered into cancer cells. This work highlights the great potential of NIR-absorbing polymeric nanoparticles as multifunctional drug carriers for potential cancer combination therapy with high efficacy.