At the age of twelve he entered the University of Heidelberg, which he left in the following year for Tübingen. After taking his master's degree in 1501, he began the study of theology under Johann Jakob Lempp, and studied the elements of Hebrew and political economy with Konrad Summenhart. He left Tübingen in 1501 on account of the plague and after a year at Cologne finally settled at Freiburg-im-Breisgau, at first as a student of theology and law and later as a successful teacher. In 1508 he entered the priesthood and two years later obtained his doctorate in theology.
At Freiburg in 1506 he published his first work, Ludicra logices exercitamenta and also proved himself a brilliant and subtle orator, although obsessed by an untamable controversial spirit and unrestrained powers of invective. At odds with his colleagues, he was glad to accept a call to a theological chair at Ingolstadt in Nov., 1510, receiving at the same time the honors and income of a canon at Eichstadt. In 1512 he be came prochancellor at the university and from that time until his death he was in complete control of the destinies of Ingolstadt, on which he impressed the character of ultracatholicism which made it a bulwark of the ancient faith in Germany.
His wide knowledge found expression in numerous writings. In the theological field he produced his Chrysopassus (Augsburg, 1514), in which he de veloped a Semi-Pelagian theory of predestination, while he obtained some fame as commentator on the Summulae of Peter of Spain and on Aristotle's De caelo and De anima. As a political economist he defended interest, despite the opposition of the bishop of Eichstadt.
As early as the spring of 1517 Eck had entered into friendly relations with Martin Luther, who had regarded him as in harmony with his own views, but this illusion was short-lived. In his Obelisci Eck attacked Luther's theses, which had been sent him by Scheurl, and accused him of promoting the heresy of the Bohemian Brethren and of fostering anarchy within the Church. Luther replied in his Asterisci adversxes obeliseos Eccii, while Carlstadt defended Luther's views of indulgences and engaged in a violent controversy with Eck.
A mutual desire for a public disputation led to a compact between Eck and Luther by which the former pledged himself to meet Carlstadt in debate at Erfurt or Leipzig, on condition that Luther abstain from all participation in the discussion. In Dec., 1518, Eck published the twelve theses which he was prepared to uphold against Carlstadt, but since they were aimed at Luther rather than at the ostensible opponent, Luther addressed an open letter to Carlstadt, in which he declared himself ready to meet Eck in debate.
The disputation between Eck and Carlstadt began at Leipzig June 27, 1519. In the first four sessions Eck maintained the thesis that free will is the active agent in the creation of good works, but he was compelled by his opponent to modify his position so as to concede that the grace of God and free will work in harmony toward the common end. Carlstadt then proceeded to prove that good works are to be ascribed to the agency of God alone, whereupon Eck yielded so far as to admit that free will is passive in the beginning of conversion, although he maintained that in course of time it enters into its rights; so that while the entirety of good works originates in God, their accomplishment is not entirely the work of God.
Despite the fact that Eck was thus virtually forced to abandon his position, he succeeded, through his good memory and his dialectic skill, in confusing the heavy-witted Carlstadt and carried off the nominal victory. He was far less successful against Luther, who, as Eck himself confessed, was his superior in memory, acumen, and learning. After a disputation lasting twenty-three days (July 4-27), Eck was greeted as victor by the theologians of the University of Leipzig, who overwhelmed him with honors and sent him away with gifts.
The impression produced by Eck upon his auditors during that momentous time may be best learned from the account of the humanist Peter of Moselle, who described him as tall, stout, and squarely built. His voice was full and rolling, and of an admirable quality for an actor, or even for a public crier, while the sum total of his features would seem to argue the butcher or the professional soldier rather than the theologian. As far as his intellectual gifts were concerned, he had a wonderful memory, which, if supplemented by other talents in like proportion, would have made him a marvel, but he lacked swiftness of apprehension and deep insight, so that his masses of arguments and citations were indiscriminate, and he was filled with an inconceivable impudence though he had the cleverness to conceal it.
Soon after his return to Ingolstadt,, Eck attempted to persuade Elector Frederick of Saxony to have Luther's works burned in public, and during the year 1519 he published no less than eight writings against the new movement. He failed, however, to obtain a condemnatory decision from the universities appointed to pronounce on the outcome of the Leipzig disputation. Erfurt returned the proceedings of the meeting to the Saxon duke without signifying its approval, while Paris, after repeated urging, gave an ambiguous decision limited to "the doctrine of Luther so far as investigated." Eck's only followers were the aged heretic-hunter Hoogstraten and Emser of Leipzig, together with the allied authorities of the universities of Cologne and Louvain. Luther returned Eck's assaults with more than equal vehemence and about this time Philipp Melanchthon wrote Œcolampadius that at Leipzig he had first become distinctly aware of the difference between true Christian theology and the scholasticism of the Aristotelian doctors. In his Excusatio (Wittenberg? 1519?) Eck, irritated all the more because early in the year he had induced Erasmus to caution the young theological student against precipitating himself into the religious conflict, retorted that Melanchthon knew nothing of theology. In his reply to the Excusatio, Melanchthon proved that he was thoroughly versed in theology, and Eck fared still worse in October of the same year, when he sought to aid Emser by a strongly-worded tirade against Luther. Two biting satires, one by OEcolampadius and the other by Pirkheimer, stung him to a fury which would be satisfied with nothing less than the public burning of the entire literature in the market-place at Ingolstadt, an act from which he was restrained by his colleague Reuchlin.
Eck was far more highly esteemed as the dauntless champion of the true faith at Rome than in Germany. In Jan., 1520, he visited Italy at the invitation of Pope Leo X, to whom he presented his latest work De primate Petri adversus Ludderum (Ingolstadt, 1520) for which he was rewarded with the nomination to the office of papal protonotary, although his efforts to urge the Curia to decisive action against Luther were unsuccessful for some time.
On June 16, however, appeared the fateful bull Exurge Domine, in which forty-one propositions of Luther were condemned as heretical or erroneous. Entrusted with the publication of the bull in Germany, Eck returned home, only to find how rapidly Luther had gained favor. At Meissen, Brandenburg, and Merseburg he succeeded in giving the papal measure due official publicity, but at Leipzig he was the object of the ridicule of the student body and was compelled to flee by night to Freiberg, where he was again prevented from proclaiming the bull. At Erfurt the students tore the instrument down and threw it into the water, while in other places the papal decree was subjected to still greater insults.
At Vienna its publication encountered grave difficulties, and Eck had good cause to set up a votive tablet to his patron saint upon his safe return to Ingolstadt, although even there only the authority of the papal mandate made the publication of the bull possible. This last humiliation was due, in great measure, to the fact that he had availed himself of the permission to pronounce the papal censure on prominent followers of the new movement besides Luther, and had thus made his office a means of personal revenge. Eck's letter to Charles V, written in Feb., 1521, seems to have had little effect upon the proceedings at the Diet of Worms.
Wealth and power were included in the aspirations of Eck. He appropriated the revenues of his parish of Günzburg, while he relegated its duties to a vicar. Twice he visited Rome as a diplomatic representative of the Bavarian court to obtain sanction for the establishment of a court of inquisition against the Lutheran teachings at Ingolstadt. The first of these journeys, late in the autumn of 1521, was fruitless on account of the death of Leo X, but his second journey in 1523 was successful. With great insight and courage he showed the Curia the true condition of affairs in Germany and pictured the general incapacity of the representatives of the Church in that country.
Of the many heresy trials in which Eck was the prime mover during this period it is sufficient to mention here that of Leonhard Kaser, whose history was published by Luther.
In addition to his inquisitorial duties, every year witnessed the publication of one or more writings against iconoclasm and in defense of the doctrines of the Mass, purgatory, and auricular confession. His Enchiridion locorum communium adversus Lutherum et alios hostes ecclesiae (Landshut, 1525) went through forty-six editions before 1576. As its title indicates, it was directed primarily against Melanchthon's Loci, although it also concerned itself to some extent with the teachings of Zwingli.
Eck offered to refute Zwingli's "heresies" in a public disputation (Aug. 13, 1524), and appeared at Baden, only 12 m. n.w. of Zurich, but in the hands of the bitterest partizans of the Roman Church, and from May 21 until June 18, 1526, the debate went on. Zwingli was not present, but supported his friends who were there by constant suggestions. The affair ended decidedly in favor of Eck, who induced the authorities to enter on a course of active persecution of Zwingli and his followers (Conference of Baden).
The effect of his victory at Baden was dissipated, however, at the Disputation of Bern (Jan., 1528), where the propositions advanced by the Reformers were debated in the absence of Eck, and Bern, Basel, and other places were definitely won for the Reformation. At the Diet of Augsburg Eck played the leading part among theologians on the Roman Catholic side.
While still at Ingolstadt Eck drafted for the use of the emperor a list of 404 heretical propositions from the writings of the Reformers, and collaborated with more than twenty Catholic theologians in writing the confutatio pontificia, in which the Catholic refutation of the Protestants was embodied. His efforts at peace, in which his readiness to meet the Reformers half-way shows him to have been sincere, failed, however, on account of the hatred and contempt with which he was regarded by the Protestant theologians.
He renewed his efforts at Worms in Jan., 1541, and succeeded in impressing Melanchthon as being quite prepared to give his assent to the main principles of Protestantism. After the meeting at Regensburg in the spring and summer of the same year, on the other hand, he exerted himself to prevent any compromise between the two theologies.
The last important phase of his activity was his conflict with Butzer, whom he attacked on account of the attitude assumed by the latter in his edition of the transactions of the Conference of Regensburg.
Special mention should be made, among Eck's many writings, of his German translation of the Bible (the New Testament a revision of H. Emser's rendering) which was first published at Ingolstadt in 1537.