Abstract Using more than three decades (1993–2024) of satellite altimetry and ocean reanalysis, we reassess the dominant timescales of low‐frequency mesoscale eddy variability along the eastern boundary of the subtropical South Indian Ocean. After removal of the seasonal cycle, eddy kinetic energy (EKE) is primarily modulated on decadal timescales (8–16 years), with a pronounced spectral peak near 10–12 years, whereas interannual variability (2–7 years) is comparatively weak. Decadal EKE variability is governed by baroclinic instability associated with vertical shear between the poleward Leeuwin Current (LC) and the equatorward Leeuwin Undercurrent. Decadal changes in LC strength dominate shear variability and are strongly linked to Pacific decadal forcing. These findings improve our understanding of the dynamics of mesoscale eddies in this dynamically distinct eastern boundary system.