Paleo‐temperature data indicates that the Earth's mantle has not cooled at a constant rate. The data show slow cooling from 3.8 to 2.5 Ga followed by more rapid cooling until the present. This has been argued to indicate a transition from a single plate mode to a plate tectonics. However, a tectonic change may not be necessary. Multistage cooling can result from deep water cycling coupled to mantle convection. Melting and volcanism removes water from the mantle (degassing). Dehydration tends to stiffen the mantle, which slows convective vigor and plate velocities causing mantle heating. Higher mantle temperature tends to lower mantle viscosity and increase plate velocities. If these two tendencies are in balance, then mantle cooling can be weak. Breaking this balance, via a switch to net mantle rehydration, can cool the mantle more rapidly. We use coupled water cycling and mantle convection models to test the viability of this hypothesis. Within model and data uncertainty, the hypothesis that deep water cycling can lead to a multi‐stage Earth cooling is consistent with data constraints. Probability distributions, for successful models, indicate that plate and plate margin strength play a minor role for resisting plate motions relative to the resistance from interior mantle viscosity. Plain Language Summary The Earth's internal energy drives geologic and tectonic activity. How the Earth's interior has cooled over time provides constraints on how this energy has been tapped. Observational constraints indicate that Earth cooling was multistaged with slow interior cooling followed by an acceleration in cooling rate. We use thermal history models to test the hypothesis that this transition is due to a change in the nature of water cycling between surface and interior reservoirs. The models indicate that water cycling, coupled to plate tectonics, can lead to multistage Earth cooling that is consistent with observational constraints. This hypothesis requires no change in the tectonic mode of the Earth—it is consistent with the idea that plate tectonics has operated over geologic history. Key Points Deep water cycle coupled to thermal convection allows for multistage Earth cooling Multistage mantle cooling does not require tectonic transitions A switch from mantle dewatering to rewatering leads to accelerated mantle cooling