G quadruplex DNA facilitates a pervasive path to homologous recombination.

Homologous recombination (HR) requires efficient homology search and strand invasion, yet how homologous templates are identified within nuclear space remains unclear. Here, we identify G-quadruplex (G4) DNA structures as pervasive effectors of template strand invasion and uncover the G4 helicase DHX36 as a potent suppressor of this process. DHX36 loss stabilizes G4s, enhances HR, and accelerates repair of replication-associated DNA breaks. G4-mediated HR depends on the non-canonical strand invasion factors RAD51AP1, WDR48, and USP1, and requires G4 motifs within the homologous repair template. DHX36 loss partially restores HR and PARP inhibitor resistance in BRCA1-deficient cells, while promoting aberrant recombination and Alternative Lengthening of Telomeres (ALT). Together, our findings establish dynamic G4 regulation as a key determinant of homology search, genome maintenance, and recombination fidelity.