Marcus Andrew Hislop Clarke FRSA (24 April 1846 – 2 August 1881) was an English-born Australian novelist, journalist, poet, editor, librarian, and playwright. He is best known for his 1874 novel For the Term of His Natural Life, about the convict system in Australia, and widely regarded as a classic of Australian literature. It has been adapted into many plays, films and a folk opera.

Marcus Clarke was born in 11 Leonard Place, Kensington, London, the only son of London barrister William Hislop Clarke and Amelia Elizabeth Matthews Clarke, who died when he was just four years old. He was the nephew of Lieutenant-Colonel Sir Andrew Clarke, a Governor of Western Australia, and grandson of a retired military medical officer, Dr Andrew Clarke, who made his fortune in the West Indies and settled in Ireland. Clarke was born with his left arm at least two inches shorter than the right, which prevented him from joining the army, though he became an accomplished diver in his days at Cholmeley Grammar, Highgate School. Clarke also had a slight stammer which remained his whole life.

Marcus Clarke was educated at Highgate School (1858–62), where his classmates included Gerard Manley Hopkins, Cyril Hopkins and E.H. Coleridge. Clarke attracted Hopkins' attention primarily due to his eloquence, leading Hopkins to describe him as a "kaleidoscopic, parti-coloured, harlequinesque, thaumatropic Being" Clarke had problems with applying himself to his schoolwork, and was deprived, in his senior year, of the poetry prize as punishment. On one hand he was considered charming and witty, but on the other spoilt, conceited and aimless which could be partially attributed to his Bohemian upbringing by this father, and the novels which he spent much of his time reading.

In 1862, father William was sent to Northumberland House suffering a mental, physical, and financial breakdown and died there a year later, leaving Clarke an orphan and without the means to live as a dilettante, which had been his expectation. The biography "Cyril Hopkins' Marcus Clarke" is the only first-hand account of Clarke's early life in London. It draws on first-hand experiences of both author and subject.

At age 17, his cousin, Andrew Clarke, suggested he emigrate to Victoria where another relative, their uncle, James Langton Clarke, was a county court judge working in Ararat. Writing from his journey to Australia, he sent Hopkins a letter describing a sunset he had witnessed; this letter probably figured as partial inspiration for Hopkins' poem "A Vision of the Mermaids". After arriving in Melbourne on 6 June 1863, Clarke was at first a clerk in the Bank of Australasia, but showed no business ability. After a year, he moved to the country and proceeded to learn farming at a station on the Wimmera River, near Glenorchy, Victoria where his uncle had an interest.

Clarke was already writing stories for the Australian Magazine, when in 1867 he joined the staff of The Argus and The Australasian in Melbourne through the introduction of Dr. Robert Lewins, writing under the heading 'The Peripatetic Philosopher'. He was noted for his vivid descriptions of Melbourne's street scenes and city types, including the "low life" of opium dens, brothels and gambling houses. He always claimed he was interested in the "parti-colored, patch-worked garment of life". These columns brought Clarke to the attention of the public, who enjoyed his schoolboy humor and his popularity as a writer grew. Clarke contributed to many colonial newspapers and he was the local correspondent for the London Daily Telegraph.

In 1868 Clarke founded the Yorick Club, which soon numbered among its members the chief Australian men of letters and 1869 he married the actress Marian Dunn (often "Marion"), daughter of actor and comedian John Dunn, with whom he had six children. Clarke wrote "two sparkling comedies" specially for Marian, A Daughter of Eve and Forbidden Fruit. One of his writing projects at this time was he and Henry Kendall working together to produce the short-lived satirical magazine Humbug (1869–70).

Clarke briefly visited Tasmania in 1870 at the request of The Argus to experience at first hand the settings of articles he was writing on the convict period. Old Stories Retold began to appear in The Australasian from February. The following month his great novel His Natural Life (later called For the Term of His Natural Life) commenced serialization in The Australian Journal (which Clarke was editing), and was later published in book form in 1874. For the Term of His Natural Life is a "ripping yarn", which at times relies on unrealistic coincidences. The story follows the fortunes of Rufus Dawes, a young man transported for a theft that he did not commit, when rendering assistance to the victim of a mugging. The harsh and inhumane treatment meted out to the convicts, some of whom were transported for relatively minor crimes, is clearly conveyed. The conditions experienced by the convicts are graphically described. The novel was based on research by the author as well as a visit to the penal settlement of Port Arthur. Clarke originally referred to the novel as "His Unnatural Life." One critic has claimed that Clarke's novel is "the book that, more than any other, has defined our perception of the Australian convict experience.". For the Term of his Natural Life is considered a novel in the grand tradition, that places Clarke with Charles Reade, Victor Hugo and Fyodor Dostoevsky among the great nineteenth-century visionaries who found in the problems of crime and punishment a new insight, especially relevant in the convict-founded Australian colonies, into the foundations of human worth.