He ruled the Austrian hereditary lands of the Habsburgs most of his public life, at the behest of his elder brother, Charles V, Holy Roman Emperor and King of Spain. Ferdinand was Archduke of Austria from 1521-1564. After the death of his brother-in-law Louis II, Ferdinand ruled as King of Bohemia and Hungary (1526–1564). When Charles retired in 1556, Ferdinand became his successor as Holy Roman Emperor, while Spain, the Spanish Empire, Naples, Sicily, Milan, the Netherlands, and Franche-Comté went to Philip, son of Charles.
Ferdinand's motto was Fiat justitia et pereat mundus ("Let justice be done, though the world perish").
Ferdinand was born on 10 March 1503 in Alcala de Henares, 40 km from Madrid, the son of the Infanta Joanna of Castile (1479–1555), the future Queen of Castile known as Joanna the Mad, and Habsburg Archduke Philip the Handsome (1478–1506), Duke of Burgundy and future King of Castile, who was heir to Emperor Maximilian I. Ferdinand shared his birthday with his maternal grandfather Ferdinand II the Catholic, King of Aragon.
Charles entrusted Ferdinand with the government of the Austrian hereditary lands, roughly modern-day Austria and Slovenia. Ferdinand also served as his brother's deputy in the Holy Roman Empire during his brother's many absences and in 1531 was elected King of the Romans, making him Charles's designated heir in the Empire. Charles abdicated in 1556 and Ferdinand succeeded him, assuming the title of Emperor elect in 1558.
After Sultan Suleiman the Magnificent defeated Ferdinand's brother-in-law Louis II, King of Bohemia and of Hungary, at the battle of Mohács on 29 August 1526, Ferdinand was elected King of Bohemia in his place. Nicolaus Olahus, secretary of Louis, attached himself to the party of King Ferdinand, but retained his position with the queen-dowager Mary of Habsburg. The throne of Hungary became the subject of a dynastic dispute between Ferdinand and John Zápolya, voivode of Transylvania. Each was supported by different factions of the nobility in the Hungarian kingdom; Ferdinand also had the support of Charles V. After defeat by Ferdinand at the Battle of Tokaj in 1527, Zápolya gained the support of Suleiman. Ferdinand was able to win control only of western Hungary because Zápolya clung to the east and the Ottomans to the conquered south. Zápolya's widow, Isabella Jagiełło, ceded Royal Hungary and Transylvania to Ferdinand in the Treaty of Weissenburg of 1551. In 1554 Ogier Ghiselin de Busbecq was sent to Istanbul by Ferdinand to discuss a border treaty over disputed land with Suleiman.
The most dangerous moment of Ferdinand's career came in 1529 when he took refuge in Bohemia from a massive but ultimately unsuccessful assault on his capital by Suleiman and the Ottoman armies at the Siege of Vienna. A further Ottoman attack on Vienna was repelled in 1533. In that year Ferdinand signed a peace treaty with the Ottoman Empire, splitting the Kingdom of Hungary into a Habsburg sector in the west and John Zápolya's domain in the east, the latter effectively a vassal state of the Ottoman Empire.
In 1538, by the Treaty of Nagyvárad, Ferdinand became Zápolya's successor. He was unable to enforce this agreement during his lifetime because John II Sigismund Zápolya, infant son of John Zápolya and Isabella Jagiełło, was elected King of Hungary in 1540. Zápolya was initially supported by King Sigismund of Poland, his mother's father, but in 1543 a treaty was signed between the Habsburgs and the Polish ruler as a result of which Poland became neutral in the conflict. Prince Sigismund Augustus married Elisabeth of Austria, Ferdinand's daughter.
The western rump of Hungary over which Ferdinand retained dominion became known as Royal Hungary. As the ruler of Austria, Bohemia and Royal Hungary, Ferdinand adopted a policy of centralization and, in common with other monarchs of the time, the construction of an absolute monarchy. In 1527 he published a constitution for his hereditary domains (Hofstaatsordnung) and established Austrian-style institutions in Pressburg for Hungary, in Prague for Bohemia, and in Breslau for Silesia. Opposition from the nobles in those realms forced him to concede the independence of these institutions from supervision by the Austrian government in Vienna in 1559.
In 1547 the Bohemian Estates rebelled against Ferdinand after he had ordered the Bohemian army to move against the German Protestants. After suppressing Prague with the help of his brother Charles V's Spanish forces, he retaliated by limiting the privileges of Bohemian cities and inserting a new bureaucracy of royal officials to control urban authorities. Ferdinand was a supporter of the Counter-Reformation and helped lead the Catholic response against what he saw as the heretical tide of Protestantism. For example, in 1551 he invited the Jesuits to Vienna and in 1556 to Prague. Finally, in 1561 Ferdinand revived the Archdiocese of Prague, which had been previously liquidated due to the success of the Protestants.
Ferdinand died in Vienna and is buried in St. Vitus Cathedral in Prague.
{| class="wikitable" ! Name || Birth || Death || Notes |- | Elisabeth of Austria || July 9, 1526 || June 15, 1545 || In 1543 she was married to future King Sigismund II Augustus of Poland and Lithuania. |- | Maximilian II, Holy Roman Emperor || July 31, 1527 || October 12, 1576 || Married to his first cousin Maria of Spain and had issue. |- | Anna of Austria || July 7 1528 || October 16/October 17, 1590 || Married Albert V, Duke of Bavaria. |- | Ferdinand II, Archduke of Austria || June 14, 1529 || January 24, 1595 || Married to Philippine Welser and then married his niece Anne Juliana Gonzaga. |- | Maria of Austria || May 15 1531 || December 11 1581 || Consort of Wilhelm, Duke of Jülich-Cleves-Berg. |- | Magdalena of Austria || August 14, 1532 || September 10, 1590 || A nun. |- | Catharine of Austria || September 15, 1533
|- |- |- |- |- |- |-