Born Mary Anne Madden in Cootehill, Co Cavan, Sadlier published roughly sixty novels and numerous stories. She wrote for Irish immigrants in both the United States and Canada, encouraging them to attend mass and retain the Catholic faith. In so doing, Sadlier also addressed the related themes of anti-Catholicism, the An Gorta Mór, emigration, and domestic work. Her writings are often found under the name Mrs. J. Sadlier.
Upon the death of her father, Francis, a merchant, Mary Madden emigrated to Sainte-Marthe, Quebec in 1844, where she married publisher James Sadlier, also from Ireland, on 24 November 1846. Sadlier published much of her work in the family’s Catholic magazine, The Tablet. While living in Canada, Sadlier published eighteen books—five novels, one collection of short stories, a religious catechism and nine translations from French—in addition to assorted magazine articles she contributed to the Pilot and American Celt free of charge.
After moving to New York in 1860, she produced 26 books, including 14 novels, within nine years. Sadlier apparently donated her articles out of sympathy with the nationalistic causes of Irish journals. In addition to the novels already discussed, during her stay in Montreal Sadlier also wrote two novels set in Ireland: Alice Riordan; the Blind Man’s Daughter (1851) and New Lights; or, Life in Galway (1853). In New Lights, Sadlier deals with An Gorta Mór for the first time. The book proved one of her most popular, going through at least eight editions in fifty years. In this novel, Sadlier focuses a polemical attack on the Protestant practice of converting Irish peasants by promising them soup, but condemns peasant retaliation and violence.
In the early 1860s, the couple moved to New York City. The Sadlier’s New York home became the hub of literary activity in the Catholic community, and Sadlier also enjoyed the company of the brightest Irish writers in the United States and Canada, including New York Archbishop John Hughes, editor Orestes Brownson and Thomas D’Arcy McGee. She held weekly salons in her Manhattan home, as well as her summer home on Far Rockaway. Her closest friend was D’Arcy McGee, a poet, Irish nationalist exile and Canadian statesman known as one of the founding “Fathers of Confederation” who helped bring about Canada’s independence. McGee and Sadlier shared an interest in a “national poetry” that would not only capture the spirit of a people, but inspire them to political and national independence. While McGee, as a man, could take part in political rallies and organise Irish-American support for Home Rule, Sadlier, as a woman, directed her support for Irish independence into literature. McGee’s associates in “Young Ireland” included Samuel Ferguson, who in the words of one critic “become a link with the Irish Literary Revival of Yeats’s generation “and were the founders of the Dublin newspaper the Nation”. McGee’s biographer notes that Sadlier’s success inspired him to write emigrant novels, and was planning a novel on this subject at the time of his death. McGee’s controversial politics cost him his life, when an Irish-American radical who opposed McGee’s shift to the right assassinated him in 1868. McGee, who sorely missed the Sadlier family after their move to New York in 1860, had been planning a visit when he was shot. His death was “a crushing blow to Mrs. Sadlier and her husband, who were his enthusiastic friends”. Sadlier edited a collection of McGee’s poetry in 1869 in tribute to his memory.
She remained in New York for nine years before returning to Canada, where she died in 1903. In later years she lost the copyright to all her earlier works, many of which remained in print.