In the context of paucity for suitable granular soils at various work sites, it has become inevitable for the use of marginal soils (low quality soils) and has been being used for different types of constructions. With the advent of reinforcing soil, a wide variety of materials such as geosynthetics are used for reinforcement. Apart from geosynthetics, coir fiber is also been used for soil strength improvement for their engineering practice. Coir fiber is randomly distributed in soil mass for the purpose of reinforcement. Fly ash has been used at several work sites due to its abundant availability as a waste material. The effective use of Fly ash has an advantage over saving and preserving natural resources, leading in the reduction in cost of the project. Apart from various other techniques of soil modification such as chemical stabilization, lime stabilization etc; the cement modification has got prominence. In the present study, the marginal soil is treated with 3% cement that could able to make it non–plastic. An attempt was made to investigate the effectiveness of coir fiber as reinforcement for locally available cement modified marginal soil and mixed with Fly ash. The intention of the work is to study the effectiveness of coir fiber as a randomly distributed reinforcement on shear strength and strength characteristics of cement modified marginal soil mixed with Fly ash. A series of laboratory tests such as direct shear and unconfined compressive strength tests were conducted using marginal soil. The shear strength of this marginal soil reinforced with 2% coir and mixed with 10% Fly ash was 1.5 to 2 times the shear strength of plain marginal soil. Hence, the experimental study provides an approximate solution for enhancement of shear strength of marginal soil, that marginal soil could be used in construction of reinforced soil structures.