Nano materials based on poly(ionic liquid)s (PILs) have been extensively studied in recent decades due to their unique abilities in morphological control and applications in catalysts. The self-assembly of PILs enables the formation of diverse nanostructures (such as spheres or vesicles), typically exhibiting high specific surface areas, which are highly desirable in catalysis. This review first summarizes common synthetic methods for PILs and then focuses on explaining the principles of PIL self-assembly and strategies for morphology control, while also comparing different self-assembly approaches. Furthermore, from a macroscopic perspective, applications of PILs in catalysis are discussed, coupled with particular emphasis on comparing their roles in composite materials, highlighting their irreplaceable function in heterogeneous catalytic systems. Finally, current research challenges and perspectives on future developments of PILs are also presented.