Nanointerfacial decoration of silver nanoparticles (AgNPs) is an ideal protocol to improve the antibacterial efficiency of diverse nanomaterials, including carbon nanotube (CNT), graphene, and many other intensively studied nanoarchitectures, which provides a tremendous possibility for designing advanced antibacterial biomaterials and biomedical devices. However, the direct exposure of AgNPs will lead to potential mammalian cell apoptosis and death, which significantly limits their biological applications. In this study, we demonstrated a green and one-step approach to achieve robust antibacterial and highly biocompatible AgNP-CNT composites. AgNPs were produced via mussel-inspired "one-step" in situ reduction and coating process and were anchored onto the surface of a CNT. Simultaneously, protective polymer layers were formed to shield the AgNPs to improve their biocompatibility. Because of the bactericidal efficiency of AgNPs, the composites showed robust antibacterial efficiency in terms of both inhibition of bacterial cell growth and bacterial killing activity. Moreover, owing to the shielding effects of the polymer coatings, the nanocomposites exhibited much improved compatibility with human umbilical vein endothelial cells compared with bare AgNP-CNTs. Furthermore, the nanocomposites exhibited good stability in psychological solutions. With integrated excellent antibacterial activity, cell compatibility, and long-term stability, it is believed that the synthesized AgNP-CNT composites will be of promising potential in antibacterial applications. Meanwhile, the proposed strategies can also be applied to fabricate many other kinds of AgNP-based composites because of the versatile functionality of catecholic polymers.