Monolayers of transition metal dichalcogenides (TMDCs) are atomically thin direct-bandgap semiconductors with potential applications in nanoelectronics, opto-electronics, and electrochemical sensing. Recent theoretical and experimental results have suggested that they are ideal systems for exploiting the valley degrees of freedom of Bloch electrons. Here, we report detailed studies of the opto-valleytronic properties of a chiral histidine molecule embedded in monolayer MoS2 single crystals grown via chemical vapor deposition. By irradiating MoS2 with circularly polarized light and measuring the resulting spatially resolved circularly polarized emission, we find the existence of a significantly increased circular polarization for D-histidine doped MoS2. The increased valley contrast is attributed to the selective enhancement of both the excitation and emission rates having one particular handedness of the circular polarization. These results provide a promising pathway to enhance the valley contrast for monolayer TMDCs at room temperature.