Frictional heating during earthquake rupture raises the fault‐zone fluid pressure, which affects dynamic rupture and seismic radiation. Here, we investigate two key parameters governing thermal pressurization of pore fluids – hydraulic diffusivity and shear‐zone half‐width – and their effects on earthquake rupture dynamics, kinematic source properties, and ground motions. We conduct 3D strike‐slip dynamic rupture simulations assuming a rate‐and‐state dependent friction law with strong velocity weakening coupled to thermal‐pressurization of pore fluids. Dynamic rupture evolution and ground shaking are densely evaluated across the fault and Earth’s surface to analyze the variations of rupture parameters (slip, peak slip rate, rupture speed, and rise time), correlations among rupture parameters, and variability of peak ground velocity. Our simulations reveal how variations in thermal‐pressurization affect earthquake rupture properties. We find that the mean slip and rise time decrease with increasing hydraulic diffusivity, whereas mean rupture speed and peak slip‐rate remain almost constant. Mean slip, peak slip‐rate, and rupture speed decrease with increasing shear‐zone half‐width, whereas mean rise time increases. Shear‐zone half‐width distinctly affects the correlation between rupture parameters, especially for parameter pairs (slip, rupture speed), (peak slip‐rate, rupture speed), and (rupture speed, rise time). Hydraulic diffusivity has negligible effects on these correlations. Variations in shear‐zone half‐width primarily impact rupture speed, which then may affect other rupture parameters. We find a negative correlation between slip and peak slip‐rate, unlike simpler dynamic rupture models. Mean peak ground velocities decrease faster with increasing shear‐zone half‐width than with increasing hydraulic diffusivity, whereas ground‐motion variability is similarly affected by both the parameters. Our results show that shear‐zone half‐width affects rupture dynamics, kinematic rupture properties, and ground shaking more strongly than hydraulic diffusivity. We interpret the importance of shear‐zone half‐width based on the characteristic time of diffusion. Our findings may inform pseudodynamic rupture generators and guide future studies on how to account for thermal‐pressurization effects.