Although his status as second son did not suggest that Luís would ascend to the Portuguese throne, his education was meticulous and largely shared with his older brother, the Royal Prince Pedro: he was tutored by the counsellor Carl Andreas Dietz, who had been his father Fernando's preceptor until April 1847, when Dietz was forced to leave Portugal on charges of meddling in national politics associated with his Protestant religious affiliation, and was replaced by the Viscount of Carreira, assisted by Manuel Moreira Coelho.

[1] As the second-born son of the royal couple, Luís embarked on a naval career, having been appointed private in the Company of the Marine Guards and recognized in a ceremony at the Navy Arsenal on October 28, 1846, when he was only 8 years old.

He had his first naval command in September 1857, on the brig Pedro Nunes, in which he made a cruise off the coast of Portugal and a trip to Gibraltar.

Commanding the Bartolomeu Dias, he completed nine service missions between 1858 and 1860: he led the expedition to the archipelagos of Madeira and the Azores; he was responsible for transporting Prince George of Saxony to Lisbon, where he married Infanta Maria Ana, his sister; took the couple to England; traveled to Tangier; and, in 1860, Angola; he went to Madeira again on the orders of Empress Elisabeth of Austria; and brought Prince Leopold of Hohenzollern-Sigmaringen from Southampton, for his wedding with Infanta Antonia, then took the bride and groom to Anvers.

[1] D. Luís inherited the crown in November 1861, succeeding his brother Pedro V as he left no descendants, and was acclaimed king on 22 December of the same year.

On 27 September of the following year, he married Maria Pia of Savoy, daughter of King Vitor Emanuel II of Italy, by proxy.

After the Glorious Revolution deposed Isabel II of Spain in September 1868, the new Cortes began the task of searching for a suitable liberal-leaning candidate from a new dynasty to replace her.

If Luís accepted the Spanish crown, he would have to abdicate in Portugal to Carlos, his son of only 6 years, with Ferdinand II as regent, opening up the possibility of an Iberian Union in the medium term.

[2][3] During his reign, and as a result of the creation of the general consumption tax, which was poorly received by public opinion, a riot called Janeirinha broke out (at the end of 1867).

The governments at various times were composed by the Progressistas (Liberals) and the Regeneradores (Conservatives), the party generally favoured by King Luís, who secured their long term in office after 1881.

He invested a large part of his fortune in financing scientific projects and oceanographic research vessels, which travelled the oceans in search of specimens.

[5][4] In June 1862, Luís asked Archduchess Maria Theresa of Austria (1845–1927), a daughter of Archduke Albert, Duke of Teschen and Princess Hildegard of Bavaria, to marry him in a letter sent to her father.