We report a tunable, single-pass, pulsed nanosecond difference-frequency generation (DFG) source based on the new semiconductor nonlinear material, orientation-patterned gallium phosphide (OP-GaP). The DFG source is realized by mixing the output signal of a nanosecond OPO tunable over 1723–1827 nm with the input pump pulses of the same OPO at 1064 nm in an OP-GaP crystal, resulting in tunable generation over 233 nm in the mid-infrared from 2548 to 2781 nm. Using a 40-mm-long crystal, we have produced ∼14  mW∼14  mW of average DFG output power at 2719 nm for a pump power of 5 W and signal power of 1 W at 80 kHz repetition rate. To the best of our knowledge, this is the first single-pass nanosecond DFG source based on OP-GaP. The DFG output beam has a TEM00TEM00 spatial mode profile and exhibits passive power stability better than 1.7% rms over 1.4 h at 2774 nm, compared to 1.6% and 0.1% rms for the signal and pump, respectively. The OP-GaP crystal is recorded to have a temperature acceptance bandwidth of 17.7°C.