Marine microorganisms represent virtually unlimited sources of novel biological compounds and can survive extreme conditions. Cellulases, a group of enzymes that are able to degrade cellulosic materials, are in high demand in various industrial and biotechnological applications, such as in the medical and pharmaceutical industries, food, fuel, agriculture, and single-cell protein, and as probiotics in aquaculture. The cellulosic biopolymer is a renewable resource and is a linearly arranged polysaccharide of glucose, with repeating units of disaccharide connected via beta-1,4-glycosidic bonds, which are broken down by cellulase. A great deal of biodiversity resides in the ocean, and marine systems produce a wide range of distinct, new bioactive compounds that remain available but dormant for many years. The marine environment is filled with biomass from known and unknown vertebrates and invertebrate microorganisms, with much potential for use in medicine and biotechnology. Hence, complex polysaccharides derived from marine sources are a rich resource of microorganisms equipped with enzymes for polysaccharides degradation. Marine cellulases' extracts from the isolates are tested for their functional role in degrading seaweed and modifying wastes to low molecular fragments. They purify and renew environments by eliminating possible feedstocks of pollution. This review aims to examine the various types of marine cellulase producers and assess the ability of these microorganisms to produce these enzymes and their subsequent biotechnological applications.