A major issue in the development of more sustainable fiber-reinforced cementitious composites is the control of the fiber-matrix interaction. In this study, ultra-high molecular weight polyethylene microfibers are surface-modified using two bio-based materials, dopamine and chitosan. Both coatings add polar groups to the surface of the initially nonpolar and non-reactive fibers; the combination of dopamine with chitosan may improve the alkaline stability of the films. Confocal and atomic force microscopy (AFM) depict changes of the surface morphology; zeta potential measurements show variations of the chemical surface properties of the fibers after modification. Unmodified and modified fibers are embedded in a novel LC³ matrix; the interaction between fibers and concrete matrix is studied by single fiber pullout tests. The thin polydopamine film improves both the wettability and the interfacial shear stress and pullout energy of the fibers in the cement matrix. The combined dopamine + chitosan coating exhibits a slightly weaker fiber-matrix adhesion.