CRYSTALS-Dilithium is a lattice-based post-quantum digital signature scheme that is resistant to attacks by quantum computers and has been selected to be standardized in the NIST post-quantum cryptography (PQC) standardization process. However, the speed performance and design flexibility of the Dilithium still need to be evaluated. This article presents a high-performance software/hardware co-design of CRYSTALS-Dilithium based on the NIST PQC round-3 parameters. High-speed pipelined hardware modules for NTT/INTT, point-wise multiplication/addition, and for SHAKE are included in the design to accelerate the time-consuming operations in Dilithium. All hardware modules are parameterized, thus allowing full support of runtime configuration to increase versatility. Moreover, the proposed software/hardware architecture and tight operating workflows reduce the data transmission overhead between the processor and other hardware modules. The hardware accelerator is implemented with a reconfigurable logic on FPGA and is integrated with the high-performance ARM Cortex-A9 processor in the Xilinx Zynq Architecture. We measure the performance of the software/hardware system for Dilithium in NIST security levels 2, 3, and 5. Compared to pure software implementations, we achieve 8.7–12.5 times speedup in Key generation, 6.3–7.3 times speedup in Sign, and 9.1–12.2 times speedup in Verify operations.