[10] At the beginning of the 1860s the Emperor of Brazil, Pedro II, sought to marry his daughters, Princesses Isabel and Leopoldina, to ensure his succession.

Turning to his European relatives, the emperor asked his sister Princess Francisca and her husband to advise him on young princes who could marry his daughters.

[11][12] Desiring to follow the successful navy career of his father (who would retire as a vice-admiral), Prince Pierre expressed his wishes to his family.

After graduation from the academy, Prince Pierre received an honorary appointment as an acting ensign in the Union Navy on 28 May 1863 and served on the corvette USS John Adams, a training ship for midshipmen in Newport; he joined its crew while it was part of the South Atlantic Blockading Squadron, stationed off Morris Island inside Charleston Bar.

[18] Since France remained closed to the Orléans family due to the post-revolution Exile Law of 28 May 1848, Prince Pierre obtained permission (with his father's help) to serve for two years as an officer of the watch on the Bartolomeu Dias, a Portuguese naval ship on a mission in the Pacific.

With his relative and childhood friend, Count Ludovic de Beauvoir and Albert-Auguste Fauvel, he embarked on a merchant ship for a tour of the Pacific from 1865 to 1867;[20] the three traveled to Australia, Java, Siam, China, Japan and California.

[18] With the fall of the Second French Empire on 4 September 1870 Prince Pierre could return to France and become part of its Navy, which was marginally active during the Franco-Prussian War (primarily fought on land).

[21] Upon his entry into service for France, he was appointed lieutenant aboard the newly built (1870) frigate L'Océan under the command of Admiral Renault.

Despite the scandal caused by his relationship with Lebesgue, Prince Pierre remained close to his family and regularly visited his sister, Princess Françoise.

[1] Fond of hunting, the prince also frequented the forest of Arc-en-Barrois (a wilderness area in the Chaumont Arrondissement owned by him and his family, with a large game population).