Composite solid electrolytes are attractive as they combine the high ionic conductivity of ceramic nanoparticles and the excellent mechanical properties of polymer electrolytes. Vertically aligned ceramic nanoparticles in the polymer matrix represent an ideal structure for maximizing ionic conductivity of composite electrolytes. The ice-templating method was used to build rechargeable solid-state lithium metal batteries with a vertically aligned ceramic/polymer composite electrolyte composed of high ionic conductivity Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and polyethylene oxide (PEO) polymer. The vertical LAGP walls provide continuous channels for fast ionic transport, while the PEO matrix renders the composite electrolyte flexible. This solid-state composite electrolyte has a conductivity of 1.67 × 10−4 S cm−1 at room temperature and 1.11 × 10−3 S cm−1 at 60 °C. LiFePO4 (LFP)/vertically aligned LAGP- PEO/Li full cells were also developed with a high capacity retention of 93.3% after 300 cycles. This study demonstrates the successful application of vertically aligned ceramic/polymer composite electrolytes for solid-state batteries with high performance.