In this work, we report a high thermal conductivity (k) of 162 W m⁻¹ K⁻¹ and 52 W m⁻¹ K⁻¹ at room temperature, along the directions perpendicular and parallel to the c-axis, respectively, of bulk hexagonal BC₂P (h-BC₂P), using first-principles calculations. We systematically investigate elastic constants, phonon group velocities, phonon linewidths and mode thermal conductivity contributions of transverse acoustic (TA), longitudinal acoustic (LA) and optical phonons. Interestingly, optical phonons are found to make a large contribution of 30.1% to the overall k along a direction perpendicular to the c-axis at 300 K. BC₂P is also found to exhibit high thermal conductivity at nanometer length scales. At 300 K, a high k value of ∼47 W m⁻¹ K⁻¹ is computed for h-BC₂P at a nanometer length scale of 50 nm, providing avenues for achieving efficient nanoscale heat transfer.