In November 1562 Maximilian was chosen King of the Romans, or German King, by the electoral college at Frankfurt, where he was crowned a few days later, officially designating him heir to the empire. After assuring the Catholic electors of his fidelity to their faith, and promising the Protestant electors that he would publicly accept the confession of Augsburg when he became emperor, he also took the usual oath to protect the Church, and his election was afterwards confirmed by the papacy.
Maximilian was the first King of the Romans not to be crowned in Aachen. In September 1563 he was crowned King of Hungary by the Archbishop of Esztergom, Nicolaus Olahus, and on his father’s death, in July 1564, he became Maximilian II, Holy Roman Emperor and King of Hungary, Croatia and Bohemia. He was also Archduke of Austria.
The new emperor had already shown that he believed in the necessity for a thorough reform of the Church. He was unable, however, to obtain the consent of Pope Pius IV to the marriage of the clergy, and in 1568 the concession of communion in both kinds to the laity was withdrawn. On his part Maximilian granted religious liberty to the Lutheran nobles and knights in Austria, and refused to allow the publication of the decrees of the council of Trent.
Amidst general expectations on the part of the Protestants he met his first summoned Diet of Augsburg in March 1566. He refused to accede to the demands of the Lutheran princes; on the other hand, although the increase of sectarianism was discussed, no decisive steps were taken to suppress it, and the only result of the meeting was a grant of assistance for the war with the Turks, which had just been renewed.
The Ottomans would besiege and conquer Szigetvár in 1566, but their sultan, Suleiman I the Magnificent, would die of old age during the siege. With neither side winning a decisive engagement, Maximilian’s ambassadors Antun Vrančić and Christoph Teuffenbach would meet with the Ottoman Grand Vizier Sokollu Mehmed Pasha in Adrianople to negotiate a truce in 1568.
The terms of the Treaty of Adrianople required the Emperor to recognise Ottoman suzerainty over Transylvania, Wallachia, and Moldavia. In his realm, Suleiman I was the tenth and longest-reigning Sultan of the Ottoman Empire from 1520 until his death in 1566. Under his administration, the Ottoman caliphate ruled over at least 25 million people.
Meanwhile, the relations between Maximilian II and Felipe II of Spain had improved, and the emperor’s increasingly cautious and moderate attitude in religious matters was doubtless because the death of Felipe II’s son, Don Carlos, had opened the way for the succession of Maximilian, or of one of his sons, to the Spanish throne. Evidence of this friendly feeling was given in 1570, when the emperor’s daughter, Archduchess Anna, became the fourth wife of Felipe II. Archduchess Anna was Felipe’s niece, her mother, Infanta Maria of Spain, was Felipe’s sister. Maximilian II, Holy Roman Emperor and Infanta Maria of Spain, were first cousins.
In 1570 the emperor met the diet of Speyer and asked for aid to place his eastern borders in a state of defence, and also for power to repress the disorder caused by troops in the service of foreign powers passing through Germany. He proposed that his consent should be necessary before any soldiers for foreign service were recruited in the empire; but the estates were unwilling to strengthen the imperial authority, the Protestant princes regarded the suggestion as an attempt to prevent them from assisting their co-religionists in France and the Netherlands, and nothing was done in this direction, although some assistance was voted for the defense of Austria.
The religious demands of the Protestants were still unsatisfied, while the policy of toleration had failed to give peace to Austria. Maximilian’s power was very limited; it was inability rather than unwillingness that prevented him from yielding to the entreaties of Pope Pius V to join in an attack on the Turks both before and after the victory of Lepanto in 1571; and he remained inert while the authority of the empire in north-eastern Europe was threatened.
In 1575, Maximilian was elected by the part of Polish and Lithuanian magnates to be the King of Poland in opposition to Stephan IV Bathory, but he did not manage to become widely accepted there and was forced to leave Poland.
Emperor Maximilian II died on October 12, 1576 in Regensburg while preparing to invade Poland. On his deathbed he refused to receive the last sacraments of the Church. He is buried in St. Vitus Cathedral in Prague.
By his wife Maria he had a family of ten sons and six daughters. He was succeeded by his eldest surviving son, who had been chosen King of the Romans in October 1575, and was elected as Holy Roman Emperor Rudolf II. Another of his sons, Matthias, also became Holy Roman Emperor Emperor; three others, Ernst, Albert and Maximilian, took some part in the government of the Habsburg territories or of the Netherlands, and a daughter, Elizabeth, married Charles IX of France.