Henry III, Duke of Brunswick-Lüneburg (* 1416 Grubenhagen, † 20 December 1464[1]), of the House of Welf, was a Duke of Brunswick-Lüneburg ruling the ducal Principality of Grubenhagen between 1427 and 1464.
Henry was the eldest son of Eric I, Duke of Brunswick-Grubenhagen and Elizabeth of Brunswick-Göttingen, a daughter of Otto the Bad, Duke of Brunswick-Göttingen.
Until his coming of age in 1437 he was under the guardianship of Duke Otto II of Brunswick-Grubenhagen-Osterode.
In the year 1447 a feud broke out between Henry and Louis I, Landgrave of Hesse, who was allied with the Archbishop of Mainz and the dukes of Göttingen.
Louis and his allies besieged Grubenhagen Castle, but despite the deployment of two cannon, had to withdraw again.