Ferdinand I (12 January 1751 – 4 January 1825) reigns variously over Naples, Sicily, and the Two Sicilies from 1759 until his death.

He is the third son of King Charles III of Spain (also King of Naples and Sicily) by his wife Maria Amalia of Saxony.

On 10 August 1759, Charles succeeds his elder brother, Ferdinand VI, as King Charles III of Spain.

Treaty provisions make Charles unable to hold all three crowns.

On 6 October 1759, he abdicates in favor of his son Ferdinand (Charles's eldest son Philip has learning difficulties and the second son, Charles, becomes the heir to the Spanish throne).

Ferdinand is the founder of the Two Sicilies branch of the House of Bourbon.