Freestanding　gallium　nitride　(GaN)　membranes　can　extend　the　applications　of　GaN　to　more　functional　devices　through　heterogeneous　integration.　Two-dimensional　(2D)　materials　provide　a　versatile　platform　for　the　preparation　of　a　freestanding　ultrathin　membrane.　However,　fabrication　of　a　freestanding　GaN　membrane　with　the　aid　of　2D　materials　presents　a　challenge　at　the　GaN/2D　interface:　keeping　strong　epitaxial　interactions　for　epitaxy　while　contrarily　ensuring　weak　interactions　for　intact　exfoliation.　Here,　an　approach　for　achieving　a　freestanding　GaN　membrane　is　demonstrated　via　epitaxy　of　GaN　on　chemical　vapor　deposition　(CVD)-grown　nearly　single-crystalline　bilayer　graphene/sapphire,　followed　by　intact　exfoliation.　Single-crystalline　GaN　is　realized　by　inheriting　the　lattice　orientation　of　graphene　in　a　quasi-van　der　Waals　epitaxy　mode　and　modulating　the　growth　kinetics　of　III-nitrides.　Subsequently,　controllable　exfoliation　is　realized　at　the　bilayer　graphene　interface　by　adjusting　the　interface　adhesion.　The　achieved　freestanding　GaN　membrane　maintains　a　high　quality　comparable　to　that　of　GaN　on　a　rigid　substrate.　This　work　offers　a　promising　strategy　for　the　fabrication　of　a　high-quality　freestanding　GaN　membrane　for　diverse　device　applications.