A three-dimensional (3D) numerical investigation is carried out to examine the effect of magnetic field (MF) on laminar forced convection of ferrofluids. Laminar flow (Reynolds number (Re) ≤ 100) of ferrofluid is modeled in a square mini-channel of 2 mm hydraulic diameter in the presence of the MF. A magnetic force is induced in ferrofluids because of the applied MF, which accelerates the upstream flow and decelerates the downstream flow with respect to the magnet's location. The acceleration/deceleration of the flow disrupts the hydrodynamic and thermal boundary layers (BLs), positively affecting the heat transfer. The extent of magnetic influence primarily depends on the Reynolds number and induced magnetic force. At low Re (= 25), where magnetic force dominates over inertial force, the flow of ferrofluid is strongly affected by the MF. This results in a higher augmentation in convective heat transfer. As the Re of the flow is increased to Re = 75, the inertial forces partially overcome the effect of the magnetic force, resulting in a smaller augmentation. The interaction of magnetic and inertia forces is expressed through a dimensionless magnetic Froude number (). The effect of volumetric concentration of nanoparticles, Reynolds number, and the presence of multiple magnets placed along the flow channel on heat transfer is investigated through a parametric study. A correlation has also been proposed to predict the net enhancement in the Nusselt number due to the application of the MF based on the results of the present study.