Polymeric graphitic carbon nitride materials have attracted significant interest in recent years and found applications in diverse light-to-energy conversions such as artificial photosynthesis, CO₂reduction or degradation of organic pollutants. However, their utilization in synthetic photocatalysis especially in the direct functionalization of C(sp³)−H bonds remains underexplored. Herein, we report mesoporous graphitic carbon nitride (mpg-CN) as a heterogeneous organic semiconductor photocatalyst for direct arylation of sp³ C−H bonds <i>via </i>a combination of<i> </i>hydrogen atom transfer and nickel catalysis. Our protocol has a broad synthetic scope (>70 examples including late-stage modification of densely functionalized bio-active molecules), is operationally simple, and shows high chemo- and regioselectivity. Facile separation and recycling of the mpg-CN catalyst in combination with its low preparation cost, innate photochemical stability and low toxicity are beneficial features overcoming typical shortcomings of homogeneous photocatalysis. Additionally, mechanistic investigations indicate that an unprecedented energy transfer process (EnT) from the organic semiconductor to the nickel complex is operating.