Stable graphene oxide monoliths (GOMs) have been fabricated by exploiting epoxy groups on the surface of graphene oxide (GO) in a ring opening reaction with amine groups of poly(oxypropylene) diamines (D400). This method can rapidly form covalently bonded GOM with D400 within 60 s. FTIR and XPS analyses confirm the formation of covalent C-N bonds. Investigation of the GOM formation mechanism reveals that the interaction of GO with a diamine cross-linker can result in 3 different GO assemblies depending on the ratio of D400 to GO, which have been proven both by experiment and molecular dynamics calculations. Moreover, XRD results indicate that the interspacial distance between GO sheets can be tuned by varying the diamine chain length and concentration. We demonstrate that the resulting GOM can be moulded into various shapes and behaves like an elastic hydrogel. The fabricated GOM is non-cyctotoxic to L929 cell lines indicating a potential for biomedical applications. It could also be readily converted to graphene monolith upon thermal treatment. This new rapid and facile method to prepare covalently cross-linked GOM may open the door to the synthesis and application of next generation multifunctional 3D graphene structures.