The increased level of industrial pollutants in water and drug resistant pathogens are serious threat to human and aquatic life. Graphene based materials are an attractive choice due to numerous fascinating features of graphene. However, combining graphene with other nanomaterials in the form of nanocomposites give a window of opportunities to fabricate and investigate new materials. Herein, a set of four graphene based nanocomposites are presented that are combination of graphene and metal/non-metal oxides. These nanocomposites are synthesized, systematically characterized and are compared for their performance in environmental and biomedical applications. As a start-up, synthesis, the physio-chemical characterizations, photocatalytic and antibacterial properties of MgO and graphene nanoplatelets (GNPs) nanocomposites are presented. The crystallinity, phase, morphology, chemical bonding, and vibrational modes of prepared nanomaterials are studied. The conducting nature of GNPs is tailored via photocatalysis and enhanced antibacterial activity. It is interestingly observed that the MgO/GNPs nanocomposite with optimized GNPs content shows a significant photocatalytic activity (97.23% degradation) as compared to bare MgO (43%) which makes it the potential photocatalyst for purification of industrial waste water. In addition, the effect of increased quantity of GNPs on antibacterial performance of nanocomposites against pathogenic microorganisms is researched, suggesting them toxic. MgO/GNPs 25% nanocomposite may have potential applications in waste water treatment and nanomedicine due its multifunctionality. In the following chapter, immobilization of monodispersed silicon dioxide (SiO2) nanoparticles on multiple graphene layers is demonstrated for intercalation of graphene nanoplatelets. The exceptional conducting nature of graphene makes it a viable candidate for enhancing the effectiveness of photocatalytic and biomedical nanomaterials. Interestingly, the addition of graphene nanoplatelets with SiO2 nanoparticles enhances the photocatalytic efficiency from 46% to 99%. For biomedical applications, it is found that 75% of Gram positive and 50% of Gram negative bacteria have been killed; hence, bacterial proliferation is significantly restricted. The prepared nanocomposites with a controlled amount of carbon in the form of graphene can be employed for photocatalysis based waste water remediation and biomedicine. However, the photocatalytic and antibacterial performance obtained up to this stage of work is moderate only. An effective, fast and economic dye removal method is essential to meet the stringent economic requirements. Therefore, graphene/Fe3O4 nanocomposite is chosen. This nanocomposite obtained via soft chemical method is characterized for its crystallinity, morphology, microstructure, vibrational modes and magnetic properties. Graphene sheets decorated with magnetite nanoparticles are investigated for their photocatalytic response against methyl orange. The study reveals that the conducting nature of graphene, engineered bandgap and photo Fenton like reaction synergistically govern the efficient photocatalytic activity of nanocomposite. Interestingly, it is observed that methyl orange can be completely removed i.e., upto 99.24% by graphene/Fe3O4 nanocomposite (Fz) in 30 min only, whereas the removal efficiency is 43% for Fe3O4 nanoparticles, alone. The presence of graphene endows the delay in charge carriers’ recombination whereas, photo Fenton like reaction stimulates the generation of reactive oxygen species. This ultimately leads to the highly enhanced photocatalytic activity and complete removal of methyl orange. The magnetically separable photocatalyst, presented in this work, offers great prospects for fast and economical decontamination of dye polluted water. The antibacterial performance is also significantly enhanced but a complete pathogen control is not achieved. At final stage, NiO nanoflakes and graphene/NiO nanocomposite are synthesized. A study on their crystal phase analysis and morphology is presented. In addition, HRTEM images, SAED patterns and Raman modes are also investigated. A solar light induced dye removal and bactericidal properties of nickel oxide (NiO) and GNPs nanocomposites are presented. The conducting nature of GNPs is the key factor that governs the enhanced photocatalytic and antibacterial activity. It is interestingly found that the graphene/NiO nanocomposite shows outstanding photocatalytic activity (99% degradation) as compared to NiO (34%) alone, which makes it potential candidate for depollution of dye contaminated water. In addition, the optimized concentration of GNPs in graphene/NiO nanocomposite, renders it as an exceptional antibacterial material with 100% growth inhibition of pathogenic microorganisms (both Gram positive and Gram-negative bacteria). Therefore, graphene/NiO nanocomposite can be an innovative material to achieve complete pathogen control alongside being an economic solution for water treatment.