Novel multicomponent fibers that include single-walled carbon nanotubes (SWNT) and lysozyme (LSZ) are reported. These fibers exhibit antibacterial and mechanical properties suitable for fabrics, clothing and technical textiles in medical environments. The challenging combination of several components in a single fiber material is achieved via fundamental studies on the phase behavior of aqueous LSZ–SWNT dispersions. The addition of molecular cationic surfactants proved to be critical to achieving stable liquid mixtures that can be spun into fibers. In the absence of the cationic surfactant tetradecyl trimethylammonium bromide (TTAB), depletion effects result in large aggregates at relatively low SWNT concentration. However, the addition of TTAB increases the concentration at which demixing occurrs by approximately one order of magnitude. Dry-spun fibers with significant antibacterial activity and toughness are obtained from LSZ–TTAB–SWNT dispersions combined with a polyvinyl alcohol (PVA) solution. Toughness is strongly affected by the initial dispersion state. The most remarkable fibers are produced from concentrated LSZ–TTAB–SWNT supernatants; they both have four times the toughness of spider silk and 70% of the native LSZ activity.