Mont-Bernanchon is a commune in the Pas-de-Calais department in the Nord-Pas-de-Calais region of France.
Mont-Bernanchon situated some 5 miles (8.0 km) north of Béthune and 27 miles (43.5 km) west of Lille, at the junction of the D937 and D184 roads. Both the Clarence River and the Canal d’Aire flow by the commune, which covers a large area of forests and lakes.