MgO/hydromagnesite blends have emerged as promising low-carbon alternatives to conventional building materials based on Portland cement. Despite recent advancements in the characterisation and modelling of Mg-bearing phases in this type of binder, the durability of building products, i.e. mortar and concrete, has received comparatively little attention. This study investigates the ability of MgO/hydromagnesite binders to resist chloride and moisture ingress and to protect embedded steel from corrosion. A combination of chloride-resistance, impedance and linear polarisation resistance measurements is used. Irrespective of the curing conditions, 90/10 mass-% MgO/hydromagnesite mortars feature a low chloride diffusion coefficient of \(D=\left(0.6\pm 0.3\right)\times {10}^{-12}\)  m2/s. Single frequency impedance measurements between stainless steel bars embedded in mortar prisms suggest that the mortars are resistant to the ingress of water, prospectively due to their dense microstructure. Embedded carbon steel bars exposed to the ingress of water and concentrated chloride-containing solutions experience low corrosion current densities in the order of 10–7 to 10–8 A/cm2, similar to the corrosion rate of passive steel in concrete. Even though the pore solution in the MgO/hydromagnesite binder is buffered at significantly lower pH (10.5–11.0) than the aqueous phase in equilibrium with portlandite in Portland cement, the novel binder could thus be used for reinforced cement products. Further testing is needed to assess the long-term stability as well as the corrosion rate of steels embedded in MgO/hydromagnesite building materials under the simultaneous ingress of moisture and CO2.