Photoresponsive ligands for G-quadruplex oligonucleotides (G4) offer exciting opportunities for the reversible regulation of these assemblies with potential applications in biological chemistry and responsive nanotechnology. However, achieving the robust regulation of G4 ligand activity with low-energy visible light sources that are easily accessible and compatible with biological systems remains a significant challenge to realizing these applications. Herein, we report the G4-binding properties of a photoresponsive dithienylethene (DTE). We demonstrate the first example of G4-specific acceleration of the photoswitching kinetics of a small molecule and the visible-light mediated switching of the G4 ligand binding mode in physiologically-relevant conditions, which in turn allows control over the G4 tetrad structure of telomeric G4 in potassium buffer. The process is fully reversible and avoids the need for high-energy UV light. This affords an efficient, practical and biologically-relevant means of control that may be applied in the generation of new responsive G4/ligand supramolecular systems.