Born in Tønder, Schleswig, in 1830 Bahnsen began his study of philosophy and (under Gregor Wilhelm Nitzsch) philology in Kiel.

From 1849 he fought as a volunteer against the Danes in the First War of Schleswig (1848–1851) and fled to Tübingen in the Kingdom of Württemberg after the disarming of Schleswig-Holstein's army in 1850.

The real-dialectical side of his teachings Bahnsen laid down in the paper On the Philosophy of History (1871), his central work The Contradiction in the Knowledge and Being of the World (1880/82), and his anniversary publication to the jubilee of the city Tübingen The Tragical as World Law and Humour as Aesthetic Shape of the Metaphysical (1877).

At the beginning of his delve into philosophy, Julius Bahnsen developed an interest in Hegelianism, which was in decline yet still popular in early 19th century Germany.

In Bahnsen's view, there was a stark mismatch between the unconcealed irrationality of the world and the naive theories, rationalizations and explanations of various philosophers.

The dialectic explained the ingrained opposition of the world with itself in a cycle of perpetual conflict (as Heraclitus had observed in his fragments centuries earlier).

He accepted a "modified" form of Hegel's dialectic, but by removing the metaphysical driving entity, there remained a void to be filled in his worldview.

After carefully examining this magnum opus and discussing it personally with the Frankfurt philosopher, Bahnsen realized that the metaphysical notion of an irrational will underlying all of creation was just what he needed in his own system.

Bahnsen had always harbored an interest in psychology, specifically the method of examination of individual characters and temperaments.

Hartmann placed Schopenhauer's idea of an ever-desiring will within the unconscious psyche of the subject, while accepting Hegel's underlying rationalism and historicism.

In contrast, Bahnsen rejected Hegel's rationalism and accepted his dialectic in a negative form, while integrating it with a pluralized version of Schopenhauer's metaphysics of will.

Whilst Bahnsen criticized Hartmann, claiming that his "Hegelian rationalism" corrupted the teachings of Schopenhauer's essentially purposeless will.

As for Hartmann, he did not accept Bahnsen's theories and diagnosed him with a psychopathic melancholy and a philosophical inability to distinguish "conflict" from "contradiction".

In his 2016 work Weltschmerz: Pessimism in German Philosophy, 1860-1900 the American professor of philosophy Frederick C. Beiser expresses Bahnsen's theory of tragedy as follows:The very heart of tragedy, for Bahnsen, consists in two fundamental facts: first, that the individual has to choose between conflicting duties or incommensurable values; and second, that he or she will be punished, or have to suffer, because he or she obeys one duty or honours one value at the expense of another.

[citation needed] A few years before Nietzsche developed his perspectivism and Kierkegaard wrote that all choices lead to sorrow and regret,[11] Bahnsen had already foreseen these conclusions.

For him, the ideas of idealism are inherently solipsistic and do not take into consideration the unique reality of the individual wills of other people.

He stated that the pessimist preserves his "idealist heart" but utilizes the "cold calculation of the head" to strike a middle ground.

Bahnsen was critical of "hedonistic" pessimism - the position that the pains of the world outnumber its pleasures in quality and quantity.

There are other reasons to be pessimistic about the world, he claimed: To realize that all moral aims and ideals are futile, yet to pursue them nonetheless, knowing full well that there is no exit or salvation — that is true pessimism.