Composite filaments are of considerable interest in research due to their exceptional performance characteristics and broad applicability. In this study, highly electrically conductive composite filaments comprising cellulose nanofibrils (CNF) and silver nanowires (AgNWs) are carefully prepared, accompanied by the proposition of an integrated microwave‐microfluidic synthesis method for AgNWs. The proposed reaction system exhibits a remarkable capability for swift AgNW synthesis, with a space‐time yield of 1.2 × 104 g (h·m3)−1, approximately five times superior to that achievable through conventional batch reactor methodologies. The microwave‐assisted microfluidic synthesis of AgNWs introduces a novel aspect to the extensive research on 1D nanomaterials. The design of experiments and multi‐objective Bayesian optimization are integrated iteratively to converge toward the global optimum, aiming to enhance screening efficiency and achieve a balanced outcome by maximizing aspect ratio and minimizing size for AgNWs. The AgNWs synthesized under optimal conditions has a diameter of ≈50.4 nm and an aspect ratio of ≈555. Subsequently, they are integrated into composite filaments with CNF, resulting in electrical conductivity and tensile strength of the composite filaments at values of 8.35 × 105 S m−1 and 186 MPa, respectively, surpassing those reported in existing literature for other analogous materials.