Ferdinand was born in Sada Palace, Sos del Rey Católico, Kingdom of Aragon, as the son of John II of Aragon (whose family was a cadet branch of the House of Trastámara) by his second wife, Juana Enríquez. He married Infanta Isabella, the half-sister and heiress of Henry IV of Castile, on 19 October 1469 in Valladolid, Kingdom of Castile and Leon. Isabella also belonged to the royal House of Trastámara, and the two were cousins by descent from John I of Castile. They were married with a clear prenuptial agreement on sharing power, and under the joint motto “tanto monta, monta tanto.” He became jure uxoris King of Castile when Isabella succeeded her deceased brother in 1474 to be crowned as Queen Isabella I of Castile. The two young monarchs were initially obliged to fight a civil war against Joan of Castile (also known as Juana la Beltraneja), the purported daughter of Henry IV, and were swiftly successful. When Ferdinand succeeded his father as King of Aragon in 1479, the Crown of Castile and the various territories of the Crown of Aragon were united in a personal union. For the first time since the 8th century, this union created a single political unit referred to as España (Spain), the root of which is the ancient name Hispania. The various states were not formally administered as a single unit, but as separate political units under the same Crown. (The legal merging of Aragon and Castile into a single Spain occurred under Philip V in 1707–1715.)

The first years of Ferdinand and Isabella’s joint rule saw the Spanish conquest of the Nasrid dynasty of the Emirate of Granada (Moorish Kingdom of Granada), the last Islamic al-Andalus entity on the Iberian peninsula, completed in 1492.  The completion of the Reconquista was not the only significant act performed by Ferdinand and Isabella in that year. In March 1492, the monarchs issued the Edict of Expulsion of the Jews, also called the Alhambra Decree, a document which ordered all Jews either to be baptised and convert to Christianity or to leave the country. That document was signed with the defeated Moorish Emir of Granada Muhammad XII, who had bargained for the Muslims of Spain to be left alone.[citation needed] It allowed Mudéjar Moors (Islamic) and converso Marrano Jews to stay, while expelling all unconverted Jews from Castile and Aragon (most Jews either converted or moved to Islamic lands of North Africa and the Ottoman Empire). 1492 was also the year in which the monarchs commissioned Christopher Columbus to find a westward maritime route for access to Asia, which resulted in the Spanish arrival in the Americas.  In 1494 the Treaty of Tordesillas divided the entire world beyond Europe between Portugal and Castile (Spain) for conquest and dominion purposes – by a north–south line drawn down the Atlantic Ocean.

Ferdinand violated the 1492 Alhambra Decree peace treaty in 1502 by dismissing the clearly guaranteed religious freedom for Mudéjar Muslims. Ferdinand forced all Muslims in Castile and Aragon to convert, converso Moriscos, to Catholicism, or else be expelled. Some of the Muslims who remained were mudéjar artisans, who could design and build in the Moorish style. This was also practised by the Spanish inquisitors on the converso Marrano Jewish population of Spain. The main architect behind the Spanish Inquisition was King Ferdinand II. Ferdinand destroyed over ten thousand Arabic manuscripts in Granada alone, burning them.  The latter part of Ferdinand’s life was largely taken up with disputes with successive Kings of France over control of Italy, the so-called Italian Wars. In 1494, Charles VIII of France invaded Italy and expelled Alfonso II, who was Ferdinand’s first cousin once removed and stepson of Ferdinand’s sister, from the throne of Naples. Ferdinand allied with various Italian princes and with Emperor Maximilian I to expel the French by 1496 and install Alfonso’s son, Ferdinand, on the Neapolitan throne. In 1501, following the death of Ferdinand II of Naples and accession of his uncle Frederick, Ferdinand signed an agreement with Charles VIII’s successor, Louis XII, who had just successfully asserted his claims to the Duchy of Milan, to partition Naples between them, with Campania and the Abruzzi, including Naples itself, going to the French and Ferdinand taking Apulia and Calabria. The agreement soon fell apart and, over the next several years, Ferdinand’s great general Gonzalo Fernández de Córdoba fought to take Naples from the French, finally succeeding by 1504.

After Isabella I’s death in 1504, her kingdom went to their daughter Joanna. Ferdinand II served as the latter’s regent during her absence in the Netherlands, ruled by her husband Archduke Philip. Ferdinand attempted to retain the regency permanently, but was rebuffed by the Castilian nobility and replaced with Joanna’s husband, who became Philip I of Castile. After Philip’s death in 1506, with Joanna supposedly mentally unstable, and her and Philip’s son, the future Emperor Charles V, only six years old, Ferdinand resumed the regency, ruling through Francisco Jiménez de Cisneros, the Chancellor of the Kingdom. Charles I (to later become Holy Roman Emperor Charles V) became the King of Aragon in 1516, with his mother Joanna as Queen in name, upon Ferdinand’s death.  Ferdinand disagreed with the policies and foreignness of Philip I. Ferdinand remarried to Germaine of Foix on October 19, 1505 in Blois, Kingdom of France, the granddaughter of his half-sister Queen Eleanor of Navarre and niece of Louis XII of France. His hope to father a new heir of Aragon, separating it from Castile, was not realised. It would have denied his son-in-law Philip I, and his grandson Charles I, from inheriting the crown and governance of Aragon. A son, John, Prince of Girona, was born on May 3, 1509, but died within hours. John was buried in the convent of Saint Paul in Valladolid, Kingdom of Castile and Leon, and later transferred to Poblet Monastery, Vimbodí i Poblet, Catalonia, Kingdom of Aragon, traditional burial site of the kings of Aragon.

Ferdinand also had children from his mistress, Aldonza Ruiz de Iborre y Alemany of Cervera. He had a son, Alonso de Aragón (born in 1469), who later became Archbishop of Saragossa, and a daughter Joanna (born in 1471), who married Bernardino Fernández de Velasco, 1st Duke of Frías.  In the 16th century his son Alonso de Aragón, found a hidden study under Ferdinand’s palace containing over 400 documents written by Ferdinand. In these documents Ferdinand explained his general outlook on political power, and his true goals behind all his decisions during life as the King of Castile and Aragon. Also through these documents, Ferdinand wrote that “during times of very complicated decision making he blindfolded himself to concentrate on the true matter of a situation, and not let other things ‘cloud his judgment’.”  In 1508 war resumed in Italy, this time against the Republic of Venice, which all the other powers with interests on the Italian peninsula, including Louis XII, Ferdinand II, Maximilian, and Pope Julius II joined together against as the ‘League of Cambrai’. Although the French were victorious against Venice at the Battle of Agnadello, the League of Cambrai soon fell apart, as both the Pope and Ferdinand II became suspicious of French intentions. Instead, the ‘Holy League’ was formed, in which now all the powers joined together against Louis XII and France.  In November 1511 Ferdinand II and his son-in-law King Henry VIII of England signed the Treaty of Westminster, pledging mutual aid between the two against Navarre and France ahead of the Castilian invasion of Navarre as of July 1512. After the fall of Granada in 1492, he had manoeuvred for years to take over the throne of the Basque kingdom, ruled by Queen Catherine of Navarre and King John III of Navarre, also lords of Béarn and other sizeable territories of the Pyrenees and western Gascony. Ferdinand annexed Navarre first to the Crown of Aragon, but later, under the pressure of Castilian noblemen, to the Crown of Castile. The Holy League was generally successful in Italy, as well, driving the French from Milan, which was restored to its Sforza dukes by the peace treaty in 1513. The French were successful in reconquering Milan two years later, however.  Ferdinand II died on January 23, 1516 in Madrigalejo, Extremadura, Kingdom of Aragon. He is entombed at Capilla Real, Granada, Kingdom of Castile and Leon. Isabella I, Joanna I, and Philip I are beside him there.

Ferdinand and Isabella established a highly effective sovereignty under equal terms. They utilised a prenuptial agreement to lay down their terms. During their reign they supported each other effectively in accordance to his joint motto of equality: “Tanto monta (or monta tanto), Isabel como Fernando”, (“They amount to the same, Isabel and Ferdinand”). Isabella and Ferdinand’s achievements were remarkable: Spain was united, or at least more united than it ever was, the crown power was centralised, at least in name, the reconquista was successfully concluded, the groundwork for the most dominant military machine of the next century and a half was laid, a legal framework was created, the church reformed. Even without the benefit of the American expansion, Spain would have been a major European power. Columbus’ discovery set the country on the course for the first modern world power.  During the reign of Ferdinand and Isabella, Spain pursued alliances through marriage with Portugal, Habsburg Austria, and Burgundy. Their first-born daughter Isabella was married to Alfonso of Portugal, and their first-born son John was married to Margaret of Austria. However, the deaths of these children, and the death of Isabella, altered the succession plan forcing Ferdinand to yield the government of Castile to Philip of Habsburg the husband of his second daughter Joanna.

In 1502, the members of the Aragonese Cortes gathered in Zaragoza, and Parliaments of the Kingdom of Valencia and the Principality of Catalonia in Barcelona, as members of the Crown of Aragon, swore an oath of loyalty to their daughter Joanna as heiress, but Alonso de Aragón, Archbishop of Saragossa, stated firmly that this oath was invalid and did not change the law of succession which could only be done by formal legislation by the Cortes with the King. So, when King Ferdinand died on 23 January 1516, his daughter Joanna inherited the Crown of Aragon, and his grandson Charles became Governor General (regent). Nevertheless, the Flemish wished that Charles assume the royal title, and this was supported by his paternal grandfather the Holy Roman Emperor Maximilian I and by Pope Leo X. Consequently, after Ferdinand II’s funeral on 14 March 1516, Charles I was proclaimed King of Castile and of Aragon jointly with his mother. Finally, the Castilian Regent, Cardinal Jiménez de Cisneros accepted the fait accompli, and the Castilian and Aragonese Cortes paid homage to him as King of Aragon jointly with his mother.  Ferdinand’s grandson and successor Charles, was to inherit not only the Spanish lands of his maternal grandparents, but the Habsburg and Burgundian lands of his paternal family, which would make his heirs the most powerful rulers on the continent and, with the discoveries and conquests in the Americas and elsewhere, of the first truly global Empire.