Metal-metal oxide composite materials have been garnering wide attention due to their extraordinary properties and applications in several areas. Ni-NiO is an important composite; its synthesis and properties have been of increased interest with regards to prominent applications in many fields. This article provides for the first time a comprehensive review of the cutting-edge research activities that focus on rational synthesis, characterization techniques, novel properties and applications of the Ni-NiO composite. While the formation mechanism of this composite is still vague, much attention has been given to the reported formation mechanisms using different precursors in one-pot synthesis, and thus, a formation mechanism and green synthesis route have been proposed. All the applications of the Ni-NiO composite in different fields including magnetic materials, ion-lithium battery, supercapacitors and catalytic activities are also emphasized. It was proved from the available literature that metallic Ni was obtained into the skelton of NiO by the reduction process during the calcination through the production of adventitious H2 via the gasification-like process.