All-solid-state cells are safe, and have high energy densities and power densities. Sulfide-based solid electrolytes (SEs) exhibit high ionic conductivities and favorable mechanical properties allowing for the facile preparation of all-solid-state cells via simple mixing and cold-pressing processes. For practical applications, it is necessary to produce SEs and all-solid-state cells more efficiently. Herein, a novel fabrication process for homogeneous composite electrodes used in all-solid-state cells was successfully demonstrated using an infiltration technique. The Li4Ti5O12 and carbon nanotube (LTO@CNT) porous electrode was infiltrated with a precursor solution containing an argyrodite Li6PS5Br SE, and the solvent was removed by drying at 150 °C under vacuum to prepare an infiltrated SE-LTO@CNT electrode. The process without conventional mixing formed an electrochemically active interface with a large contact area and favorable conduction pathways. The all-solid-state cell with the SE-LTO@CNT electrode showed an improved capacity of 163 mAh g−1 compared to those prepared with the dry-mixed electrodes at 25 °C, and the high capacity was maintained for 500 cycles. Moreover, the cell with the SE-LTO@CNT electrode showed a reversible capacity of 100 mAh g−1 or more at 4 C-rate and 100 °C. Thus, the infiltration process is effective for the practical fabrication and application of all-solid-state cells.