More recently, natural polymers produced by living organisms have received considerable attention due to their unique properties such as eco-friendliness, biodegradability, and biocompatibility. These polymers possess similar properties to conventional plastics, making them suitable potential plastic substitutes for sustainable development and conservation of finite oil resources. Poly(lactic acid) (PLA) is comparable to commonly used plastics but is inferior, thus limited applications. However, PLA can benefit from the incorporation of various polymer components with complementary properties to yield improved physical properties. The fabrication of fully bio-based nanocomposites such as that of PLA and cellulose is of particular interest to research scientists. Incorporating organic fillers such as nanocellulose in a PLA matrix gives rise to improved composite properties. Because plant cell walls comprise semicrystalline cellulose molecules embedded in matrices, the crystalline portion of the stiff chains extracted from medicinal plants is currently exploited for potential filler roles. In this review, the use of medicinal plants in bio-based composite applications is covered. Several medicinal plants as sources of cellulose, different cellulose extraction methods, as well as the resulting fiber properties, are discussed. Although tremendous progress has been made in developing biocomposites, a lot of research still needs to be carried out.