McIntire taught himself the Palladian style of architecture from books.
While still in his early twenties Mclntire, with a skill and confidence beyond his years designed a large three-story house typical of the pre-Revolutional homes in Massachusetts, and his success brought him the patronage of one of Salem's great merchants of that period, Elias Haskell Derby. For him and his wife, the former Elizabeth Crowninshield, the young architect executed many important commissions, the first of which was the great house near Derby Wharf, begun in 1787 but abandoned three years later, before completion. In 1786 Mclntire remodelled the Benjamin Pickman house, 70 Washington Square, for Mr. Derby and in 1799 designed the family mansion on Derby Street which stood until 1815. Other notable examples of his work were the Pierce-Nichols house, still standing, and one of the most architecturally interesting in Salem, the Clifford Crowninshield home in Washington Square, 1815; the mansion at 134 Essex Street owned successively by John Gardner, Joseph White and D. Pingree, deeded to the Essex Institute in 1933; the Joseph Felt house, 151 Lafayette Street, 1809-12, destroyed in the great fire of 1914; at 134 Essex Street a house for Nathan Read which stood from 1793 until 1859, and also for Mr. Read a two and a half-story frame house at Danversport, built in 1798. The last of his houses in Salem was the Benjamin Crowninshield residence at 180 Derby Street, (1809-12), much altered and enlarged in later years, and between 1906 and 1912 occupied by the Home for Aged Women. Many of these houses were adorned by carvings from his own design.
The earliest public building in Salem ascribed to Mclntire was the Assembly Hall, 319 Federal Street, opened in 1781. It was followed by the Court House (1785) one of the most important pre-Revolutionary buildings, removed in 1839 when the Boston & Maine Railroad tunnel was built.
In the latter years of the eighteenth century a new style of architecture became popular, known as the “Federal” or "Early Republican," and originating from the designs of Charles Bulfinch of Boston. Mclntire was quick to recognize the trend, and on many of his later works adapted the new style. Among these was the Stearns Block, the first pretentious brick commercial building in Salem, erected in 1792 (demolished 1902); the South Church at Chestnut and Cambridge Streets, 1804, destroyed by fire in 1903; Hamilton Hall at No. 7 Cambridge Street, 1806-7, occupied by the Salem Assembly over more than a century; Registry of Deeds at the corner of Summer and Broad Streets, 1807, (demolished 1854), and the Archer, or Franklin Building, Mr. Mclntire's last and most ambitious undertaking, a four-story structure built 1810-11 with stores and shops on the first floor, offices and halls above.
Among the distinguished homes he designed for locations outside of his native city there should be mentioned "Oak Hall" in Peabody, a mansion-type residence dating from 1801-04, remodeled and embellished in 1813-14 by carvings by the architect's son, Samuel Field Mclntire; and the Lyman house at Waltham, cl793, altered in 1882, and restored to its original state in 1918, “an elegant country-seat, with beautifully landscaped grounds."
He married Elizabeth Field on October 10, 1778, and had one son.