The effective delivery of chemotherapeutic drugs to tumor sites is critical for cancer treatment and remains a significant challenge. The advent of nanomedicine has provided additional avenues for altering the in vivo distribution of drug payloads and increasing tumor localization. More recently, cell-derived nanoparticles, with their biocompatibility and unique biointerfacing properties, have demonstrated considerable utility for drug delivery applications. Here, we demonstrate that cell membrane-derived nanodiscs can be employed for tumor-targeted delivery. To bestow active targeting capabilities to the cellular nanodiscs, we utilize a modular functionalization strategy based on the SpyCatcher system. This enables the nanodiscs to be covalently modified with any targeting ligand labeled with a short SpyTag peptide sequence. As a proof-of-concept, a model chemotherapeutic doxorubicin is loaded into nanodiscs functionalized with an affibody targeting epidermal growth factor receptor. The resulting nanoformulation demonstrates strong tumor targeting both in vitro and in vivo, and it is able to significantly inhibit tumor growth in a murine breast cancer model.