He was the son of Fritz Barth (1856–1912), Professor of NT Theology at Berne. After studying at Berne, Berlin, Tübingen, and Marburg, Karl Barth began as a minister at Geneva (1909–11) and was then for ten years (1911–21) pastor at Safenwil (Aargau). Here, under the shadow of the war of 1914–18 and in direct relation to his pastoral responsibility, he was led to a radical questioning of the prevailing liberal theology, and wrote his ‘Commentary on Romans’ (Der Römerbrief, ‘1919’, pub. 1918). In this work he revived Pauline and Reformation themes that had been muted or omitted in liberal theology—the sovereignty of God, the finitude and sinfulness of man, eschatology, and God's judgement on human institutions and culture. The originality, critical power, and actuality of its message, particularly in the pessimism of the postwar situation, at once gave him a very wide hearing among German-speaking Protestant theologians. In 1921 he became extraordinary professor at Göttingen and later Professor at Münster i.W. (1925) and Bonn (1930).

On Hitler's accession to power and the outbreak of the ‘Church Struggle’ (1933), Barth at once threw in his lot with the Confessing Church. As a Swiss subject he enjoyed a liberty of speech not open to a German and he had a strong backing. None the less his action demanded much courage. The formulation of Confessional theology in the Barmen Declaration of 1934 was largely Barth's work. At the outset he held that National Socialism, being purely a matter of secular politics, was irrelevant to the Christian, provided the freedom of the Gospel was maintained. Later he came to the view that such neutrality was not possible, and vigorously attacked Nazism. On his refusal to take an oath of unconditional allegiance to the Führer, he was deprived of his chair. He left Germany and in 1935 became Professor of Theology at Basle, where he continued to teach until he retired in 1962.

Developing the positions already announced in Romans, Barth aimed to lead theology away from what he believed to be the fundamentally erroneous 19th-cent. synthesis between theology and culture. Theology was to be based on the Word of God communicated in the Bible, and to stand over against human philosophies. Among those who chiefly influenced his thought were the great Continental Reformers and such later thinkers as S. Kierkegaard, F. M. Dostoevsky, F. Overbeck, and the Blumhardts. Human reason, he held, has no power to attain to the knowledge of God which is given only in God's gracious revelation in Jesus Christ. This revelation comes from God to man and is contrasted with religion, which is described as man's sinful attempt to grasp God and which ends only in distortion and idolatry. Clearly this outlook rules out all natural theology and makes any dialogue with non-Christian religions virtually impossible. It also led Barth to be very critical of such figures as F. D. E. Schleiermacher, G. W. F. Hegel, and A. Ritschl, and to engage in sharp exchanges with A. Harnack.

These doctrines Barth proclaimed with passionate fervour in a style at once graphic and forceful, and in language deeply influenced by the Bible. He made them the theme of innumerable sermons and addresses, as well as of more continuous writings. In 1927 he published the beginnings of a systematic exposition of his theology in Die Christliche Dogmatik im Entwurf, 1, ‘Die Lehre vom Worte Gottes’; but he abandoned this work and a few years later began again on a vast scale. In 1932 there appeared the first volume of Die kirchliche Dogmatik, on which he was destined to be engaged for most of the rest of his life. After his retirement and a serious illness, it became impossible to complete the work according to the original plan and the final volume on ‘The Doctrine of Redemption’ was never written. Nevertheless, Barth's Church Dogmatics is by far the most detailed Protestant exposition of Christian doctrine to have appeared since the Reformation.

The vast work begins from ‘The Doctrine of the Word of God’ as the source of all revelation and the foundation of any genuinely Christian theology. But the doctrine of the Trinity is soon introduced and it becomes apparent that Barth's interpretation of the Word is made in the light of the classic theological tradition. This is clear also in his treatment of the Incarnation. Although the adverse judgements on natural theology and religion remain, Barth introduces the idea of a ‘humanity’ of God, and while this leaves the initiative in grace and revelation decisively with God, it helps to narrow the gap between God and man, seemingly unbridgeable in the early writings.

In 1945 Münster University restored the doctorate of which it had deprived Barth in 1939. In politics he now declined to take up the same hostile attitude to Communism as he had hitherto done to Nazism on the ground that the Church, which must be essentially detached from politics, cannot decide in advance that Communism is necessarily evil. He continued to act as a potent astringent influence in Protestant theology, on secondary matters (e.g. Infant Baptism) often taking up provocative and sometimes unexpected positions.

In English-speaking countries, the greatest impact of ‘the Barthian Theology’ was in the 1930s. By the 1950s, though Barth still had professed disciples, his theological influence had become widely diffused among many who did not share his particular views or comprise a specifically ‘Barthian’ movement. At the same time his personal prestige, based largely on his distinctive and forthright standpoint, gave him the position of the outstanding Protestant theologian, and perhaps the most notable Christian prophet, of his time.

Barth's other works include Das Wort Gottes und die Theologie (collected lectures, 1924; Eng. tr., 1928); Die Theologie und die Kirche (further lectures, 1928); Credo (an outline of dogmatics based on the Apostles' Creed, 1935; Eng. tr., 1936); The Knowledge of God and the Service of God (Gifford Lectures, 1937–8; pub. 1938; based on the Scottish Confession of 1560); Die kirchliche Lehre von der Taufe (1943; Eng. tr., 1948); Dogmatik in Grundriss (Lectures delivered in Bonn, 1946; pub. 1947; Eng. tr., 1949); Die protestantische Theologie im 19. Jahrhundert (1947; Eng. tr. of part as From Rousseau to Ritschl, 1959; Eng. tr. of the whole, 1972); Die christliche Lehre nach dem Heidelberger Katechismus (1948; Eng. tr., 1964).

See also Brunner, E., and Dialectical Theology.