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Design of open channel transport and flow measurement systems for highly viscous liquids requires accurate modelling of laminar free overfall. In this study, a computational fluid dynamics model was developed to investigate subcritical laminar free overfall in smooth horizontal channels with 90° isosceles triangle cross-section. Volume of fluid-based simulations were performed at different liquid discharges and viscosities, with Reynolds numbers at normal uniform depth between 5.5 and 139. Simulation results were in good agreement with verification experiments, indicating development of laminar velocity magnitude profiles while gauge pressure profiles resemble hydrostatic distribution except near the brink. The end-depth-ratio ranged between 0.80 and 0.96, reducing towards values reported for turbulent free overfall in the highest Reynolds number simulation. Existing models for critical depth, end depth discharge and free overfall jet trajectories were in satisfactory agreement above Re = 10, while producing larger deviations below this threshold due to increased viscous effects.