He was appointed
Regent of the
Duchy of Oldenburg for his incapacitated cousin
Peter Frederick William in 1785. of
Lübeck by
Jean-Laurent Mosnier, 1798 From 1785 until 1803, he also served as the last
Lutheran Prince-Bishop of
Lübeck, until that
Prince-Bishopric was
secularized as the
Principality of Lübeck and joined to Oldenburg. Following the death of Wilhelm in 1823, he himself became reigning Duke of Oldenburg. Although the Duchy of Oldenburg had been elevated to a
Grand Duchy in 1815, he refrained from using the title of Grand Duke. His son,
Augustus, was the first Duke of Oldenburg to use the style of
Grand Duke. Peter I died on 21 May 1829 in
Wiesbaden. He was
buried in the Ducal
Mausoleum in the
Churchyard of Saint Gertrude in
Oldenburg. He was succeeded by his eldest son,
Paul Friedrich August, as Grand Duke, the first of the
House of Holstein-Gottorp to use the elevated style. ==Ancestry==