Herve III, Lord of Léon was the son of Herve II of Léon and his first wife Anne of Hennebont.

Herve became Lord of Léon after his father's death around 1218.

Herve married Margaret de Châteauneuf, a younger daughter of Hugh IV de Châteauneuf, Lord of Châteauneuf-en-Thymerais, and Eleanor of Dreux, a sister of Peter Mauclerc, Duke of Brittany jure uxoris.

[1] After her elder brother's death, Margaret inherited one third of the Lordships of Châteauneuf, including the castles of Châteauneuf and Senonches.

Harvey III and Margaret had: Herve died in 1241[1] and was buried in the Abbaye Notre-Dame de Daoulas.