He was born at the Château d'Eu in France, the second son of Prince August of Saxe-Coburg and Gotha and Princess Clémentine of Orléans.

His father was a first cousin of Victoria of the United Kingdom and her consort, Prince Albert of Saxe-Coburg and Gotha.

Ludwig August and his double first cousin, the French Prince Gaston, comte d'Eu (son of Victoire, sister of August's father; and prince Louis, the brother of August’s mother) were imported to Brazil in order to marry the two daughters of the Emperor Pedro II of Brazil: Isabel, the elder, and Leopoldina, the younger.

The original plan was for August to marry Isabel and Gaston to Leopoldina, but the girls decided otherwise and the Emperor, having himself experienced the unhappinesses of an arranged dynastic marriage, agreed to their wishes.

Ludwig August and Leopoldina married in Rio de Janeiro on 15 December 1864, two months after the wedding of Isabel and Gaston.