A new palladium-catalyzed benzothiadiazine-1,1-dioxide direct arylation of C(sp²)–H bonds is described. 3-Aryl-2H-benzo[1,2,4]thiadiazine 1,1-dioxides react with various aryl iodides to give the corresponding mono-arylation products 3-(biphenyl-2-yl)-2H-benzo[1,2,4]thiadiazine 1,1-dioxides with high reactivity and regioselectivity in the presence of AgOAc. Remarkedly, the addition of TFA is crucial to improve the arylation yield.