Nicotinamide adenine dinucleotide (NAD) is the redox cofactor of many enzymes, including the vast aldehyde dehydrogenase (ALDH) superfamily. Although the function of NAD(H) in hydride transfer is established, its influence on protein structure is less understood. Herein, we show that NAD+ -binding promotes assembly of the ALDH7A1 tetramer. Multiangle light scattering, small-angle X-ray scattering, and sedimentation velocity all show a pronounced shift of the dimer-tetramer equilibrium toward the tetramer when NAD+ is present. Furthermore, electron microscopy shows that cofactor binding enhances tetramer formation even at the low enzyme concentration used in activity assays, suggesting the tetramer is the active species. Altogether, our results suggest that the catalytically active oligomer of ALDH7A1 is assembled on demand in response to cofactor availability.