A strong coupling between the field theory of dislocation mechanics and heat conduction is proposed. The novel model, called the thermal field dislocation mechanics (T-FDM) model, is designed to study the dynamics of dislocations during rapid or gradual temperature changes in a body having a heterogeneous temperature distribution; for example, such conditions occur in a heat-affected crystalline solid during an additive manufacturing process. It is based on the principles of rational thermodynamics whose main assumptions include respecting local thermodynamic equilibrium and imposing the classical Clausius-Kelvin-Planck formulation of the second law of thermodynamics. The T-FDM model is designed to operate at the length scale of individual dislocations and temperature-dependent crystallographic dislocation driving forces are derived based on global dissipation considerations. The advantages and consequences of the assumptions of the T-FDM model under rapidly changing temperatures, both spatially and temporally, are discussed. Local thermodynamic equilibrium is found to be a reasonable assumption even for high rates of change of temperature such as those occurring during an additive manufacturing process. Highlights  Strong temperature gradients during 3D-printing can trigger dislocation dynamics  A novel fully-coupled dislocation dynamics and heat conduction model is proposed  Proposed model can deal with high temperature rates during additive manufacturing  Local thermodynamic equilibrium is respected even under strong temperature rates