He was born in 1817 in the shadow of the Rock of Cashel in County Tipperary, Ireland. His father, James, died in Liverpool en route to America but his mother courageously continued the journey, arriving in New York with her family in January 1830.
For two years Denis and his brother James attended St. Peter's School in Barclay Street.
He and his brother entered the book-binding shop of Arthur & Company, and in 1836 established a similar concern of their own in Carmine Street under the name of D. & J. Sadlier & Company. They soon entered the publishing field, bringing out in 1837 an edition of Alban Butler's Lives of the Saints and in 1838 a quarto Bible.
As the business grew rapidly, they continually moved to larger quarters until finally, in 1860, they located in Barclay Street, with a branch in Montreal. As job printers, contrivers of designs for churches, publishers of Bibles, prayer books, school texts, and a Household Library of 164 titles, and as compilers of the official, annual Sadlier's Catholic Directory (1864 - 96), the firm of Sadlier became a national Catholic institution.
In 1869, on the death of James, who had supervised the publication department, Denis carried on the business alone. He passed through the panic of 1873 unscathed, but in 1879, under the pressure of financial troubles, he assigned all properties, including the dower of his wife, as a pledge to his creditors; by 1884, however, the business was readjusted and continued for several years.
In 1850 Sadlier established a residence in the anti-Catholic neighborhood of Harlem, where he became popular enough to be chosen a public school trustee, then a most unusual honor for a Catholic citizen.
In 1864 he moved to Wilton, Westchester County, where he died.
Under the name D&J Sadlier, together with his brother they published an American edition of Butler's Lives of the Saints, an American Catholic Bible, and other devotional works, and eventually a weekly Catholic newspaper, The Tablet. From June 1857 to December 1881 their New York Tablet attracted numerous writers of distinction.
A passionate, intense man of marked business integrity and of liberal charities, a trustee of Manhattan College, and a self-trained reader of good books, he won recognition in both the business and the social life of New York.
Quotes from others about the person
At the obsequies in St. Patrick's Cathedral, Monsignor Quinn declared that it was Sadlier's "chief object in life to preserve the Catholics of America from the temptation to peruse such (bad) literature by giving them attractive Catholic books, " and added, "There is hardly a Catholic book which does not bear the well-known imprint of the name which has become a household word throughout the length and breadth of the English speaking Catholic world. "
He had a wife, Julia Browne, whom he had married in 1841
