Abstract: Dual precipitation of finely dispersed, nanometre-sized ScZr-containing and MgSi-containing precipitates in Al–Mg–Si–Sc–Zr alloys to exploit the full strength potential of the system necessitates a multi-stage heat-treatment procedure, accounting for the differing diffusivities of the alloying elements and the distinct precipitation temperature regimes of the respective phases. The procedure comprises a high-temperature intermediate ageing (IA) stage to form ScZr-containing phases, and a low-temperature artificial ageing (AA) stage to precipitate MgSi-containing phases. The critical step is the solution heat treatment (SHT) in between, which dissolves the coarse MgSi-containing precipitates but preserves the ScZr-containing ones. In-situ electrical resistivity measurements were employed to determine the minimum SHT temperature and duration required for dissolving the precipitates in the Al–Mg–Si alloy, which was then integrated with the thermal stability tests on the Al–Sc–Zr alloy, and the optimised multi-stage heat treatment was applied to the combined Al–Mg–Si–Sc–Zr alloy. The evolution of various phases throughout the multi-stage heat treatment was characterised and the dual precipitation successfully achieved. Heterogeneous nucleation of ScZr-precipitates on the pre-existing coarse MgSi-precipitates was observed during IA, which subsequently also serve as nucleation sites for the fine MgSi-precipitates during AA. A substantial fraction of hardness increase from ScZr-precipitates was retained after SHT, which, however, does not linearly add to the MgSi-precipitate hardening during artificial ageing. Instead, a Pythagorean superposition law was found to represent the scenario better.