•Summary of recent significant research on developing revolutionary sustained gene delivery carriers.•Synthetic nonviral systems have innate biocompatibility and tunable surface properties in gene therapy.•Customization for controlled release profiles circumvents the need for repeated administration while maintaining high transfection efficiency.•Recombination of multicomplex polymers endows with novel properties for advanced therapeutic applications. Sustained gene delivery is of particular importance today because it circumvents the need for repeated therapeutic administration and provides spatial and temporal control of the release profile. Better understanding of the genetic basis of diseases and advances in gene therapy have propelled significant research on biocompatible gene carriers for therapeutic purposes. Varied biodegradable polymer-based architectures have been used to create new compositions with unique properties suitable for sustained gene delivery. This review presents the most recent advances in various polymeric systems: hydrogels, microspheres, nanospheres and scaffolds, having complex architectures to encapsulate and deliver functional genes. Through the recombination of different existing polymer systems, the multicomplex systems can be further endowed with new properties for better-targeted biomedical applications.