In March 1869 President Ulysses S. Grant offered Stewart the position of Secretary of the Treasury (after Joseph Seligman had declined it), but he was not confirmed by the United States Senate. One source reports that a major impediment to Stewart's appointment was a provision in the act of September 2, 1789, which established the Treasury Department, prohibiting a merchant or importer in active Business from heading the Department. Although Grant requested the two houses of Congress to override this provision, upon the objection of Charles Sumner this request was not considered in the Senate. Another source attributes Stewart's rejection to his close association with Judge Henry Hilton, his wife's cousin's husband and a member of the corrupt Tweed Ring.

After six weeks at sea, Stewart arrived at his mother's home. He became a $300 a year tutor at Isaac N. Bragg's Academy, a school for wealthy youths on Roosevelt Street, and joined an Episcopal church run by Reverend Edward Mitchell. There he met his Future wife, Cornelia Mitchell Clinch, the daughter of Susannah Banker and James Clinch, a wealthy ship chandler. Cornelia's brother Charles P. Clinch (1797–1880) was Acting Collector of the Port of New York.

Alexander Turney Stewart was born in Lisburn, Ireland, to Scottish Protestant parents on October 12, 1803. Three weeks after his birth, Stewart's farmer Father died of tuberculosis. About two years later Stewart's mother remarried and followed her new husband to America, leaving Stewart behind to be raised by his grandfather, John Torney.

Torney wanted his only grandson to become a minister in the Church of Ireland. At age seven Stewart was sent to a village school, and in 1814 entered Mr. Neely's English Academy. When Stewart's grandfather died in 1816 he was brought into the home of Thomas Lamb, an Irish Quaker.

Historians know little about Stewart's life between 1818 and 1822, except that he returned to Ireland upon receiving his grandfather's inheritance of value between US$5,000 and $10,000. The will pertaining to Stewart stated:

The store opened on September 1, 1823, just across from City Hall Park, north of Chambers Street on the opposite side of Broadway from where his later Marble Palace was to stand. Rented for $375 a year, it measured 12.5 feet wide by 30 feet deep, rather small by today's standards but average during the 19th century. A larger front section used for the Business was divided by a thin wall from a smaller back section which served as Stewart's residence.

As he rose to the top of the Retail developers, Stewart included no signs on any place of his store and did not use any advertisements until May 13, 1831. He felt that anyone who wanted to shop in his store would "know where it was located."

Stewart died as one of the richest men in New York, just behind a Vanderbilt and an Astor. Worth an estimated $50 million, Stewart, unlike New York's other wealthy men who made their millions through real estate, had earned his wealth in Retail trade. Out of the twenty-four clerks who entered A. T. Stewart & Company in 1836, six still worked for the company in 1876. To these long-term employees, Stewart showed his gratitude by leaving them more than $250,000 (equivalent to $6,000,000 in 2017) in his will.

Between 1846 and 1848, the construction and finishing details were completed of one of Stewart's most famous buildings, the "Marble Palace" at 280 Broadway. This establishment, "the cradle of the department store", sent A. T. Stewart & Company to the top of America's most successful Retailers.

Stewart had extraordinary skill in Business, and by 1848 he had built a large marble-fronted store on Broadway between Chambers Street and Reade Street, which was devoted to the wholesale branch of his Business, and the largest Retail store in the world at that time. Stewart also had branches of his company in different parts of the world and owned several mills and factories. Stewart had an annual income of US$1,843,637 in 1863. His Business success is estimated to have made him one of the twenty wealthiest people in history, with a fortune equivalent to approximately 90 billion 2012 US dollars.

"The Marble Palace" claimed to be one of the first "big stores" that sold merchandise, and was a huge financial success. In 1855 Stewart's personal fortune was estimated to be $2.25 million. In 1856 Stewart decided to expand his merchandise to include furs, "the best and most natural skins", as customers were told. In the 1850s, he also followed other Retailers such as Macy's, Lord and Taylor and B. Altman and Company to the area which was to be called "Ladies' Mile", on Broadway and Sixth Avenue between 9th Street and 23rd Street.

However, in 1862, Stewart's "true" department store, referred to as the "Iron Palace", was built. This six-storey building with its cast-iron front, glass dome skylight and grand emporium, employed up to 2,000 people. The immense structure occupied a major portion of a city block near Grace Church, from Broadway and Ninth Street to Tenth Street and Astor Place. The establishment's nineteen departments included silks, dress goods, carpets, and toys.

Beginning in 1868, Stewart began receiving letters from women in rural parts of the United States requesting his merchandise. Stewart promptly replied to these letters and orders by sending out the requests and even paying the postage. Once received, women would send back the money needed to pay for their orders.

In 1869 and 1870 A. T. Stewart built the first of the grand Fifth Avenue palaces, on the North West corner of 34th Street, across from the doyenne of New York society, Caroline Schermerhorn Astor. His Architect, as for the store, was John Kellum. When all of Fifth Avenue was of brownstone rowhouses, Stewart's fireproof structure in French Second Empire style was faced with marble.

Stewart incorporated the Central Railroad of Long Island in 1871 and completed it in 1873, running from Long Island City through his development at Garden City to a brick yard at (Old) Bethpage and docks at Babylon. This became part of the Long Island Rail Road system in 1876, and the parts that have not been abandoned are the Hempstead Branch and Central Branch. The brickyard continued into existence until 1981, variously known as Bethpage Brickworks, Queens County Brick Manufacturing Company, and (after Nassau County split from Queens County in 1899) Nassau Brick Company.

The bulk of the Stewart fortune, willed to Mrs. Stewart with Judge Henry Hilton as trustee, was the subject of protracted litigation, although a swarm of long-lost Turney relatives were quickly dismissed. Claims were based in part on Mrs. Stewart's hasty transfer of the dry goods Business in 1876 to Hilton, in exchange for the $1,000,000 willed to Hilton, who carried on the Business under the name E. J. Denning & Co.

By 1877 it had expanded to thirty departments, carrying a wide variety of items. As noted by The New York Times, "a man may fit up his house there down to the bedding, carpets and upholstery."

The body of Stewart was stolen from its tomb, between nine o'clock on the evening of November 6, and daylight on the morning of November 7, 1878, 2 years, 6 months, 24 days after his burial at St. Mark's Church in-the-Bowery. The remains were held for $20,000 ransom. The ransom was paid and remains were returned, although never verified as his. A local legend states that the mausoleum holding his remains is rigged with security devices which will cause the bells of the Cathedral to ring if ever disturbed.

On the death of Stewart's widow in 1886, it was rented as premises for the Manhattan Club and was portrayed in paint in 1891 by Childe Hassam The structure was razed in 1901 to make way for the new premises of the Knickerbocker Trust Company.

On May 1, 1890, a notice appeared in the New York Times announcing Joseph Pulitzer, Julius Chambers, et al. had been indicted for posthumous Criminal libel against Alexander T. Stewart. The newspaper reprinted a letter to District Attorney Fellows citing statements in an April 14–19 series of articles in the New York World accusing Stewart of "a dark and secret crime", as the man who "invited guests to meet his mistresses at his table", and as "a pirate of the dry goods ocean."

In 1896, the Iron Palace was bought by John Wanamaker and reopened as "Wanamaker's". The Philadelphian Wanamaker had long been an admirer of Stewart and stated that one of his best qualities was his "personal attention to the details of the Business... He could have had others to look after the details — they have to be looked after, but few attend to sweeping up, and that's what Stewart did." In 1917 the New York Sun newspaper bought Stewart's Marble Palace for its main offices. In 1966 the building was designated a landmark by the City of New York.

Mrs. Stewart, who lived quietly in New York and at the Grand Union Hotel (Saratoga Springs, New York), which she inherited, died of pneumonia October 25, 1886, and ex-Judge Hilton died there 24 August 1899.