Grain boundary (GB) microstructure and microchemistry in 7xxx aluminium alloys have a great impact on their mechanical and electrochemical properties. The quench sensitivity of 7xxx aluminium alloy thick plates results in a variation of GB precipitate distribution and morphology due to varying cooling rates through the plate thickness. This study aims to model the effect of cooling rate on the nucleation and growth of the GB η-precipitate in 7xxx aluminium alloys. In order to accurately describe the thermodynamics and kinetics of the complex Al-Zn-Mg-Cu multi-component system, a CALPHAD database was directly incorporated into a phase-field framework, to simulate, with high fidelity, the evolution of GB microstructure and microchemistry during the quenching of AA7050, AA7085 and AA7449 alloys. The model predicts a stronger quench sensitivity in AA7449 and AA7050 compared to AA7085. On increasing the cooling rate from 2.5 ℃/s to 30 ℃/s, the average GB η-precipitate size is observed to decrease rapidly from 197±82 nm to 51±18 nm in AA7449. Solute depletion adjacent to the GB, resulting from quench-induced precipitation, was largely determined by the high rate of Zn and Mg diffusion. The size of the solute depletion zone reduces with increasing the cooling rates, and will affect the development of precipitate free zones during the early stages of ageing. Using AA7050 as a baseline, the influence of alloy chemistry on GB η-precipitate was also investigated by systematically varying the Cu content and Zn/Mg ratio. Increasing Cu content and the Zn/Mg ratio results in a higher solvus temperature, which benefits both the nucleation and growth of η-precipitates and leads to a higher quench sensitivity.