Heir to the throne
Lunalilo died without an heir in 1874. In the election that followed, Leleiohoku's brother, David Kalākaua, ran against Emma, the dowager queen of Kamehameha IV. On February 12, 1874, the legislative assembly voted thirty-nine to six in favor of Kalākaua over Emma. The legislature's choice of Kalākaua and the subsequent announcement caused a riot at the courthouse. To quell the civil disruption, American and British troops were landed from three warships in the harbor with the permission of the Hawaiian government, and the rioters were arrested.
Plans were discussed to marry Leleiohoku to Queen Emma, who was eighteen years his senior; she refused such a match.
After the 1874 election, King Kalākaua concerned himself with establishing a line of succession to the throne since he and his wife Kapiʻolani were childless. In the absence of legitimate children, Article 22 of the 1864 Constitution gave the monarch the power to appoint a successor or heir with the consent of the House of Nobles. Thus, Leleiohoku was named the heir apparent to the throne and publicly proclaimed as such on February 14, 1874. He was also granted the title of Prince and style of "His Royal Highness". King Kalākaua also gave royal titles and styles to their sisters, Princess Lydia Kamakaʻeha Dominis and Princess Miriam Likelike Cleghorn.
He also became a member of the Privy Council of State, an advisory body for the king, and the House of Nobles, the upper chamber of the legislature. He sat in on, and participated in, the legislative assembly of 1876 during the regular session from April 29 to September 30.
Kalākaua went on a state visit the United States from 1874 to 1875 to negotiate the Reciprocity Treaty of 1875, becoming the first reigning monarch to do so. While the king was absent, Leleiohoku ruled as regent from November 17, 1874, to February 15, 1875.
An accomplished musician, Leleiohoku founded several royal choral societies including the Kawaihau Glee Club. During the regency period, Leleiohoku’s group would compete with the singing troupes organized by his sisters Liliʻuokalani and Likelike. In later life, Liliʻuokalani admitted that "those of Prince Leleiohoku were really in advance of those of his two sisters, although perhaps this was due to the fact that the singing-club of the regent was far superior to any that we could organize; it consisted in a large degree of the very purest and sweetest male voices to be found amongst the native Hawaiians."
From 1874 to 1890, the Leleiohoku Guards, which Prince Leleiohoku gave his name, was formed as a volunteer company of cavalry in the army of the Kingdom of Hawaii. Leleiohoku served as the captain of this regiment during his lifetime.
The ranks of this regiment, along with the other known volunteer companies, were composed mainly of Hawaiian and part-Hawaiian officers with a few white officers. Each unit was subject to call for active service when necessary. An 1888 military act passed by the legislature reduced the size of the army to four volunteer companies: the Honolulu Rifles, the King's Own, the Queen's Own, the Prince's Own, and the Leleiohoku Guard. In 1890, another military act further restricted the army to just the King's Royal Guards effectively abolishing the Leleiohoku Guards.
