The complexation of MgII with adenosine 5′-triphosphate (ATP) is omnipresent in biochemical energy conversion, but is difficult to interrogate directly. Here we use the spin-urn:x-wiley:14337851:media:anie202207137:anie202207137-math-0001 β-emitter 31Mg to study MgII-ATP complexation in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) solutions using β-radiation-detected nuclear magnetic resonance (β-NMR). We demonstrate that (nuclear) spin-polarized 31Mg, following ion-implantation from an accelerator beamline into EMIM-Ac, binds to ATP within its radioactive lifetime before depolarizing. The evolution of the spectra with solute concentration indicates that the implanted 31Mg initially bind to the solvent acetate anions, whereafter they undergo dynamic exchange and form either a mono- (31Mg-ATP) or di-nuclear (31MgMg-ATP) complex. The chemical shift of 31Mg-ATP is observed up-field of 31MgMg-ATP, in accord with quantum chemical calculations. These observations constitute a crucial advance towards using β-NMR to probe chemistry and biochemistry in solution.