Examples of techniques for model-based parameter and state estimation for directional drilling in a wellbore operation are provided. In one example implementation according to aspects of the present disclosure, a computer-implemented method includes receiving, by a processing device, measurement data from the wellbore operation. The method further includes performing, by the processing device, an online estimation of at least one of a parameter to generate an estimated parameter and a state to generate an estimated state, the online estimation based at least in part on the measurement data. The method further includes generating, by the processing device, a control input to control an aspect in the wellbore operation based at least in part on the at least one of the estimated parameter and the estimated state. The method further includes executing a control action based on the control input to control the aspect of the wellbore operation.