Georg Milbradt, the governor of Saxony state, presented Germany's Great Order of Merit to the duke at a ceremony in the eastern city of Dresden.
Milbradt praised the duke for helping close the wounds left by the war and lauded his patronage of the Dresden Trust, a British group that raised -1.1 million (US$1.3 million) for the reconstruction of the city's Frauenkirche cathedral.
The rebuilt church, which British and U.S. firebombing raids destroyed at the end of the war, is to be dedicated on Sunday.
"It is thanks to you that many people in Britain made donations for the reconstruction of the Frauenkirche," said Milbradt, who presented the award on behalf of German President Horst Kohler.
The duke said he was "deeply moved" to receive the award, the highest possible for a foreigner who is not a head of state, reported AP.
U.S. Justice Department is acting behind the scenes to have Assange extradicted from the Ecuadorean Embassy in London, and prosecuted in the U.S.