The town is in the arrondissement of Bar-le-Duc, beside the canal that links the Rivers Rhine and Marne, fifteen kilometres to the south east of Bar le Duc: it is the administrative seat of the canton Ligny-en-Barrois. The population comprises 5,035 inhabitants (1999) and the area of Ligny is 32.26 km². The inhabitants are called in French Linéens.
A principal employer is the French Evobus motor bus assembly plant. Ligny is also the home town of the Essilor company which specialises in ophthalmic lens production.