Herein, a facile poly-L-lysine (PLL)-mediated one-pot hydrothermal approach was developed for large-scaled synthesis of Pd nanocones enclosed by the {1 1 1} facets, followed by uniformly dispersing them on graphitic carbon nitride (g-C3N4). The Pd nanocones/g-C3N4 demonstrated dramatic enhancement for photocatalytic transformation of Cr(VI) to Cr(III) via the dehydrogenation pathway under visible-light irradiation, which outperforms the {1 0 0} facets enclosed Pd nanocubes/g-C3N4, Pd black/g-C3N4, and bare g-C3N4 catalysts. Meanwhile, the as-prepared nanocomposite showed dramatically enhanced conversion up to 99.9% and improved reusable ability via the recycling test. It would advance the development of largely efficient g-C3N4 supported Pd nanocatalysts via morphology-and composition-engineering.