In 1931, Nikolaus succeeded to his father's titles and assumed the role of pretender to the Grand Duchy, until his death in 1970.

[citation needed] Nikolaus was born at Oldenburg, Grand Duchy of Oldenburg, the third child and first son of Frederick Augustus II, Grand Duke of Oldenburg (1852–1931) (son of Peter II, Grand Duke of Oldenburg and Princess Elisabeth of Saxe-Altenburg) and his wife, Duchess Elisabeth Alexandrine of Mecklenburg-Schwerin (1869–1955) (daughter of Frederick Francis II, Grand Duke of Mecklenburg-Schwerin and Princess Marie of Schwarzburg-Rudolstadt).

He was a first cousin of Queen Juliana of the Netherlands and with his wife and other family members was a guest at her 1937 wedding to Prince Bernhard of Lippe-Biesterfeld.

[1] Nikolaus married on 26 October 1921 in Arolsen to Princess Helena of Waldeck and Pyrmont (1899–1948), only daughter of Friedrich, Prince of Waldeck and Pyrmont and his wife, Princess Bathildis of Schaumburg-Lippe,[2] and they had issue.

His wife died in 1948, he married secondly on 20 September 1950 in Güldenstein to Anne-Marie von Schutzbar gennant Milchling (1903–1991), former wife of Count Bechtold von Bernstorff,[3] daughter of Rudolf von Schutzbar gen. Milchling (1853-1935) and his wife, Rose Marston (1872-1957).