House of Hanover King George III Reign 25th October 1760 – 29th January 1820 George William Frederick was born on the 4th June 1738 and died on the 29th January 1820. George III was King of Great Britain and Ireland from 1760 and then became King of the United Kingdom of Great Britain and Ireland after the union of the two countries in 1801. He was also Duke and prince-elector of Brunswick-Lüneburg (Hanover) in the Holy Roman Empire and later became King of Hanover in 1814. During the early part