Mr. Lafever settled in New York, and in 1828 was fisted in the City Directory as Carpenter and Architect. During the next year he won recognition as a contestant submitting a design in the competition for the new City Hall in Albany, and continued thereafter to practice architecture. At the start of his career Mr. Lefever published the first of his famous Hand Books, "The Young Builders’ General Instructor" (1829), followed in 1833 by ‘The Young Builders’ General Instructor" (1829), followed in 1833 by the Modern Builders Guide", "The Beauties of Architecture" in 1835, and finally in 1850, "The Architectural Instructor".
New York was in the midst of a building boom in the early 1830's, and Lafever participated in planning many residences, also several public buildings and churches, the latter designed in the Greek Revival style. Definitely ascribed to him is St. James Church in Brooklyn near Chatham Square, and the First Dutch Reformed Church (1835) with its monumental Ionic portico. His fame however rests on the several splendid Gothic Churches in Brooklyn built from his plans, outstanding examples of which were the First Unitarian, dedicated as the Church of the Saviour in 1841, Holy Trinity,, at the corner of Clinton and Montague Streets in 1844-47, considered by many his architectural masterpiece, and the Pierpont Street Baptist 1843-44. A later work, dating from 1851, was the Reformed Church on Brooklyn Heights, an interesting example of Italian Romanesque, which stood until 1938.
Mr. Lefever’s secular work, though less famous, was also important. In addition to several mansion-type homes he built outside of New York, he was architect of the Brooklyn Savings Bank, built in 1847 and razed in recent years to prepare for the Brooklyn Bridge Plaza, and the Packer Collegiate Institute on Brooklyn Heights, of English Gothic design, completed after his death in 1855.
During intermittent periods Mr. Lefever practiced in association with other New York architects-James Gallier, 1833-34; in 1835 and again between 1844 and 1850 with Charles Bell.