The first example of PdII -catalyzed γ-C(sp3 )-H functionalization of aliphatic and benzoheteroaryl aldehydes has been developed using a transient ligand and an external ligand, concurrently. A wide array of γ-arylated aldehydes were readily accessed without preinstalling internal directing groups. The catalytic mechanism was studied by performing deuterium-labelling experiments, which indicated that the γ-C(sp3 )-H bond cleavage is the rate-limiting step during the reaction process. This reaction could be performed on a gram scale, and also demonstrated its potential application in the synthesis of new mechanofluorochromic materials with blue-shifted mechanochromic properties.