Models can help to obtain the desired properties of steel by predicting when different microstructures form during phase transformations in manufacturing processes. One prominent model for low-alloy steel is the Kirkaldy–Venugopalan model but it has not been evaluated for wear-resistant ultra-high-strength steels (UHSS). A modified Kirkaldy-type model was developed in this work for the phase transformation kinetics in a wear-resistant UHSS. A modified incremental Koistinen–Marburger model was used for the martensite transformation which considers the gradual start of the transformation. The framework was validated by simulating the dilatometry experiments in a finite element model. Good agreement was obtained for the low cooling rates 2.5 to 15 °C/s yielding ferrite, pearlite, and bainite, as well as for the high cooling rates 20 to 50 °C/s yielding bainite and martensite. The model was also applied to the steel Hardox 450 where it predicted the formation of 99.7% martensite at the experimental critical cooling rate for full martensite formation of 12 °C/s found in the literature, which demonstrates the model’s capability to be used more generally on wear-resistant UHSS. The predicted hardness also captured the general trend seen in the hardness measurements.