Watchmakers and jewellers are looking for novel 18 carat (ct) gold alloys (75 wt% Au) that combine superior hardness (≥ 300 HV) and scratch resistance with the excellent ductility and machinability characteristic of traditional 18 ct Au–Cu–Ag alloys. The Au–Ti system has attracted attention due to the extremely high hardness of the intermetallic compound Ti3Au. We propose a processing route for the development of an 18 carat Au–Ti alloy based on casting with a grain refiner, followed by subsequent thermomechanical treatments. The resulting microstructures were analysed using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness measurements. After homogenisation, the TiAu matrix exhibited a grain size smaller than 100 µm, medium hardness (∼225 HV) and good ductility. Subsequent age-hardening treatments increased the hardness up to ∼415 HV, but at the expense of ductility, owing to the precipitation of Ti3Au. Cold deformation prior to ageing treatment resulted in a fine and complex microstructure and enhanced hardness to ∼600 HV, doubling the hardness of conventional 18 ct Au–Cu–Ag alloys. Additionally, the TiAu phase exhibits a martensitic transition at a temperature that depends on the precipitation state. These results highlight the potential of the 18 ct Au–Ti alloy as a new hard 18 ct gold alloy for jewellery and watchmaking applications.