We study proximity-induced unconventional superconductivity in a twisted graphene/NbSe₂ van der Waals heterostructure using the Bogoliubov-de Gennes formalism. The normal-state parameters of proximitized graphene are extracted from ab initio calculations at a twist angle of 23.4^∘, which reduces the common symmetry of the heterostructure to C₃. We construct symmetry-allowed superconducting gap functions of the graphene layer according to the irreducible representations of the C₃ group, containing singlet and triplet pairing channels and their mixtures. Computing the topological invariants as a function of the mixing parameters, we find a rich phase diagram of chiral topological superconducting phases, characterized by nonzero Chern numbers C∈{-4,-2,2,4}. While the nature of the superconducting order parameter of NbSe₂ remains debated, the formation of the van der Waals heterostructure and the related symmetry reduction can alter the relative stability of competing pairing channels, potentially stabilizing a chiral component that is proximity-induced into graphene and triggers the topological phases identified here, making the twisted graphene/NbSe₂ heterostructure a promising platform for chiral topological superconductivity detectable via quasiparticle interference imaging and transport measurements.