Abstract: Purpleback flying squid (Sthenoteuthis oualaniensis) is often used as a marine indicator species for evaluating marine ecological environments and multi-scale climate fluctuations. We constructed a Habitat Suitability Index (HSI) model based on sea surface temperature (SST) and wind speed (WS) data of the Northwestern Indian Ocean from 1951 to 2024 to reveal the composite driving effects of different climate modes over long time scales, and we systematically analyzed the influences of combined Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) events on the spatiotemporal distribution and latitudinal centroid of suitable habitats for purpleback flying squid. We found that sea surface temperature anomaly (SSTA) presented a spatial feature of cold in the northwest and warm in the southeast, while wind speed anomaly (WSA) showed abnormally strong values in the southwest and abnormally weak values in the northwest. Cross-correlation analysis showed that HSI was significantly negatively correlated with both Dipole Mode Index (DMI) and Oceanic Niño Index (ONI), and the maximum negative impacts appeared at lags of 4 and 5 months, respectively. Under the synergistic effect of climatic events, the combination of negative-phase IOD (−IOD) and La Niña promoted the expansion of suitable habitats; on the contrary, the combination of positive-phase IOD (+IOD) and El Niño caused habitats to shrink sharply to the minimum range and pushed suitable habitats to migrate toward high latitudes. It is confirmed that the interdecadal variation of purpleback flying squid habitats in the Northwestern Indian Ocean is not dominated by a single climate mode but jointly regulated by IOD and ENSO. This conclusion supplies key scientific support for the future construction of dynamic fishing ground early warning systems and transboundary quota management based on multi-scale climate monitoring.