Mathilde Blind (born Mathilda Cohen; 21 March 1841 – 26 November 1896), was a German-born English poet, fiction writer, biographer, essayist and critic. In the early 1870s she emerged as a pioneering female aesthete in a mostly male community of artists and writers. By the late 1880s she had become prominent among New Woman writers such as Vernon Lee (Violet Paget), Amy Levy, Mona Caird, Olive Schreiner, Rosamund Marriott Watson, and Katharine Tynan. She was praised by Algernon Charles Swinburne, William Michael Rossetti, Amy Levy, Edith Nesbit, Arthur Symons and Arnold Bennett. Her much-discussed poem The Ascent of Man presents a distinctly feminist response to the Darwinian theory of evolution.

Blind was born in Mannheim, Germany, the older child of a banker named Jacob Abraham Cohen and his own second wife, born Friederike Ettlinger. She had a brother, Ferdinand, two half-brothers (Meyer Jacob "Max" Cohen, from his father's first marriage, and Rudolf, from the marriage of Friederike and Karl Blind), and a half-sister, Ottilie, also from the marriage of Friederike and Karl Blind. Cohen died in 1848, the same year her mother remarried to Karl Blind, who was involved in the Baden insurrection of 1848. They immigrated to London in 1852, and it was around the time of the move that she took her stepfather's name.

In London, Blind attended the Ladies' Institute, St John's Wood, where she was a friend of future novelist Rosa Nouchette Carey. Much of the evidence for this period in Blind's life is contained in a 55-page typescript in the British Library, a fragmentary story of a precocious, rebellious girl who is expelled from the Ladies' Institute for her freethinking, and who then travels to Switzerland for a long stay with maternal relatives in Zürich, before embarking on an unaccompanied walking tour through the Alps – highly unusual at that time for a single woman. The protagonist's name in the typescript is Alma, but her experiences parallel closely those of Blind herself, and some of the names in the Zürich section of the narrative are those of people Blind actually knew in her adolescent years.

While in Switzerland she was barred as a woman from entry to lectures at the University of Zürich, but spent much time in the company of revolutionary colleagues of her mother and stepfather. She also took private lessons from the renowned philosopher and Sanscrit scholar Kuno Fischer. In 1854 Fischer had begun work on his History of Modern Philosophy: Descartes and His School, completed in 1865, which among other things had a direct influence on Friedrich Nietzsche. In Fischer's account of Baruch Spinoza and his ideas, Nietzsche recognized a kindred philosophical spirit. The two philosophers share a radical philosophy of immanence and the negation of all transcendence, a philosophical outlook also shared by Ludwig Feuerbach and by David Strauss, whose The Old Faith and the New: A Confession Blind translated 23 years after studying with Fischer. All four thinkers, and the adult Blind, reject teleology – the idea that there is an end goal or ultimate purpose to things. For them the immanent world, devoid of inherent purpose, constitutes the horizon of being and the sole possible source of value. This philosophical outlook informs all of Blind's writing, and caused the publisher of The Prophecy of St. Oran and Other Poems, Newman & Co., to withdraw the book from circulation. As William Michael Rossetti wrote to Ford Madox Brown, Newman & Co. "had got frightened by somebody about the atheistic character of the book, and had determined to sell it no more".

In 1866, Blind's brother Ferdinand failed in an attempt to assassinate Otto von Bismarck, then chancellor of the North German Confederation, and committed suicide in prison. He was motivated in part by his stepfather Karl Blind and other revolutionary exiles living in London, who were outraged by the way Bismarck treated the German states like pawns in his empire-building strategy. Many years later, Blind shared with her friend Moncure Conway the contents of a letter she had received from her brother in the spring of 1866. She and Ferdinand had been apart since 1864, when he left London in his 18th year to study in Germany. During his university years he also participated in the left-wing opposition to Bismarck, and after graduating in March 1866, during a hiking tour of Bavaria and Bohemia, he wrote to Blind describing the depth of his opposition to Bismarck: "As I wandered through the blooming fields of Germany, that were so soon to be crushed under the iron heel of war and saw the number of youths pass by that were to lose their lives for the selfish aims of the few, the thought came quite spontaneously to punish the cause of so much evil, even if it were at the cost of my life." The first, pseudonymous volume of poetry she published in the wake of Ferdinand's death (Poems, published by Claude Lake, 1867) is dedicated to her early mentor, the Italian revolutionary Giuseppe Mazzini, but the poems themselves also evoke the memory of Ferdinand. As James Diedrick remarked, the book "gains both biographical and literary significance when viewed as a 'double-voiced' volume that simultaneously celebrates Mazzini's victorious republicanism and obliquely honors Ferdinand, his ghostly double, whose squandered idealism and sacrifice haunt the margins of its pages."

Blind's early political affiliations were shaped by the foreign refugees who frequented her stepfather's house, including Giuseppe Mazzini, for whom she entertained a passionate admiration and about whom she would publish reminiscences in the Fortnightly Review in 1891. Other revolutionaries who frequent her mother and stepfather's house in St. John's Wood included Karl Marx and Louis Blanc. Her early commitment to women's suffrage was influenced by her mother's friend Caroline Ashurst Stansfeld, who was active in the British feminist movement from its origins in the 1840s. These radical affiliations are manifested in Blind's politically charged poetry, and in her own unbending commitment to reform. As Richard Garnett observed, in the society of political refugees and radicals Blind was raised in, "admiration must necessarily be reserved for audacity in enterprise, fortitude in adversity... anything breathing unconquerable defiance of the powers that were."

In the early 1870s, after abandoning the male pseudonym she used for her first volume of verse, Blind emerged as a force to be reckoned with in London's literary bohemia. In early January 1870 she delivered a lecture on Percy Bysshe Shelley at the Church of Progress in London, stressing the poet's political radicalism. In July of that year she published a review-essay on William Michael Rossetti's edition of The Poetical Works of Percy Bysshe Shelley in The Westminster Review that earned the praise of Algernon Charles Swinburne and gained her entry into a formerly all-male group of "Shelleyites" that included Swinburne, Rossetti, and Richard Garnett, a man who would remain Blind's friend and literary adviser throughout her life. A year after this essay appeared, Blind began publishing poetry and nonfiction in Dark Blue, a new Oxford-based journal that during its short run published prose and art by many of Britain's leading Pre-Raphaelites and aesthetes. Her wide-ranging publications in this journal are those of a daring feminist aesthete: she wrote sexually subversive poems about haunted lovers, an erudite essay on Icelandic poetry, and a short story exploring the corrosive effects of class divisions on human relations. In the fall of 1872, as her association with Dark Blue was ending, she began reviewing contemporary poetry and fiction for the Athenaeum, where over the next 15 years she passed judgement on a wide range of contemporary writers, ranging from William Morris to Margaret Oliphant. At the end of 1871 she published Selections from the Poems of Percy Bysshe Shelley for the Tauchnitz Collection of British Authors, containing an introductory "Memoir" of Shelley's life. In the following year, she brought out her translation of David Strauss's The Old Faith and the New: A Confession, which established her reputation as a daring freethinker, following in the footsteps of George Eliot, who had translated The Life of Jesus in 1853. The generic range of these early works (poetry, fiction, criticism, biography, translation), as well as their subject matter and themes (female autonomy and agency, anti-theism, aestheticism, the relationship of literary and political radicalism), indicates the aesthetic principles and themes that would characterize the remainder of Blind's career, while emphasizing the cosmopolitan nature of her sensibility and outlook.

Despite her diverse literary interests, Blind remained devoted to poetry, as is evident in an 1869 letter to Richard Garnett: "My only real intense life has been for a long time in writing, and when I cannot swim and float about in the enchanted waters of poetry I am like a fish out of water. I gasp and pant for want of the proper element to breathe in." Blind's visits to Scotland in the 1870s and 1880s inspired two poems of considerable compass and ambition: the narrative poem "The Prophecy of St. Oran" (published in 1881, but written some years earlier) and The Heather on Fire (1886), a denunciation of the Highland clearances. Both are full of impassioned eloquence and energy, and "The Prophecy" in particular has an ample share of the quality Matthew Arnold called "Celtic magic".