Nickel matrix composites are important materials for various engineering applications. The present paper describes the fabrication of bulk graphene-nickel (Gr-Ni) and reduced graphene oxide-nickel (rGO-Ni) composites by powder metallurgy technique using various graphene sources, namely, thermally exfoliated graphite (TEFG) and reduced graphene oxide (rGO) and the investigation of the mechanical properties of the composites. Homogeneous distribution of graphene derivatives in the composite matrices was confirmed for all compositions by XRD and Raman spectroscopy. It was proved that different Gr sources in the initial powder mixtures result in some different graphene derivatives type in the composites produced. Nevertheless, scanning electron microscopy data demonstrated that the microstructure of the samples produced using the different graphene sources is rather similar. It was shown that the mechanical properties of the composites are very sensitive to the type of graphene derivative chosen at low additive contents. TEFG addition results in the decreased values of tensile strength, ductility, and elongation for all compositions. It was shown that 0.1 wt.% of rGO addition resulted in the 34 % elongation-to-failure increase with no change in the UTS value of composite. The 0.1 wt.% rGO-Ni composite showed the increased elongation and the tensile strength value comparable to pure nickel specimen. Fractography tests revealed the difference in the mechanical behaviour of rGO-Ni and Gr-Ni composites.