Banim is born in Kilkenny, County Kilkenny on August 5, 1796. He is educated at Dr. Magrath’s Catholic school. He goes on to study for the bar, but a decline in his father’s business causes him to retire from his studies. He returns home to take over the family business, which he returns to prosperity, restoring his parents to comfort, both material and mental. In 1826 he visits John in London, making the acquaintance of many distinguished men of letters. When the struggle for Catholic emancipation is at its height, he works energetically for the cause.
Around 1822, Banim’s brother John broaches his idea for a series of national tales. He assists John in the O’Hara Tales, where he uses the name “Abel O’Hara,” and there is difficulty in allocating their respective contributions. While John is the more experienced writer, Michael provides material based on his social observations. They revise each other’s work. He writes in such hours as he can snatch from business, and is the principal author of about thirteen out of the twenty-four works attributed to the brothers, including Crohoore of the Bill-Hook, The Croppy, and Father Connell. He is amiable, unambitious, modest, and generous to a degree. He keeps himself in the background, letting his younger brother have all the honor of their joint production. In 1828 he has the honor of a visit from the Comte de Montalembert, who has read the O’Hara Tales and is then on a tour through Ireland.
When his brother John is struck down by illness, Banim writes and earnestly invites him to return to Kilkenny and share his home. “You speak a great deal too much,” he observes in one letter, “about what you think you owe me. As you are my brother, never allude to it again. My creed on this subject is, that one brother should not want while the other can supply him.” However, John remains in France, seeking medical care in Paris.
Following his brother’s death in 1842, Banim writes Clough Fionn (1852), and The Town of the Cascades (1864). In 1861 he writes prefaces and notes for a reprint of the “O’Hara” novels by the publishing firm William H. Sadlier, Inc. of New York City. Besides their desire to give a true picture of their country, still crippled and prostrate from the effects of the Penal Laws, the Banims are undoubtedly influenced by the Romantic movement, then at its height.
In 1840, Banim marries Catherine O’Dwyer with whom he has two daughters, Mathilde and Mary. Although a man of means, in less than a year he loses almost the whole of his fortune through the failure of a merchant. Poor health follows. He is appointed postmaster of Kilkenny in 1852, a position he holds until illness forces him to retire in 1873. He also serves a term as mayor. His health failing, he goes with his family to reside at Booterstown, near Dublin, where he dies on August 30, 1874. His widow is granted a civil list pension.