He was first trained as a carpenter and cabinetmaker in Berlin, 1837-1840, and Hamburg, 1840-1841. He received certificates for the completion of his apprenticeship, from Berlin on March 30, 1840, and from Hamburg on October 4, 1841. Feeling that his exceptional drawing ability indicated an architectural career rather than the trade of carpenter or cabinetmaker, he went on to the Royal Architectural School at Munich, where he studied for the year 1841-1842. From Munich he proceeded to Paris; the next five years were spent in the study of his profession under Henri Labrouste.
In 1847 Lienau was employed as a designer and draftsman for the Chemin de Fer de Paris â Lyon under A. Cendrier, the chief architect. The following year, 1848, after a brief visit to England, he settled in the New York region, where his brother Michael was already established as a successful wine merchant. On the way across he met Henry Marcotte, the fashionable New York decorator of the period, and they formed a partnership, Lienau & Marcotte. A large amount of work came to them almost at once, largely through Lienau's friend Francis Cottenet, whose family was related by marriage to many wealthy New York families, especially the Kanes, the Schermerhorns, the Wilkses, and the Joneses.
When shortly the firm split up, each partner to carry on his specialty by himself, Lienau found himself one of the most important architects of the city. His excellent training in Germany and France was in New York unique, and his wide connections gave him entrée into a large and expensive practice. Thus in 1849-50 he was architect of the Hart M. Shiff house, Tenth Street and Fifth Avenue (said to have introduced the mansard roof to America), and in the next few years of the two large adjoining houses on West Twenty-third Street for William C. (1850) and Edwin Schermerhorn (1860); all three were in a refined and delicate néo-Grec style. For his brother in Jersey City he was architect of a house (1849) which is a typical example of the current "Swiss" style, in wood, with broadly projecting eaves and gables and much decorative jigsaw work.
In Jersey City also he designed Grace Church, a simple and well-proportioned stone Gothic building. His houses--almost all large and luxurious examples--included those of DeLancey Kane, Newport (1852), Francis Cottenet, Dobbs Ferry (1852), a block-long row of houses for Mrs. Colford Jones, Fifth Avenue between Fifty-fifth and Fifty-sixth Streets, New York (1869), LeGrand Lockwood, South Norwalk (1869), Mathew Wilks, Galt, Canada (1872), his brother Michael Lienau, Duneck, Germany (1872), Walter Lewis, Newport (1880), Mr. Mosle, New York (1878), a row of houses in Jersey City for H. A. Booraem (1870), and other rows of houses on Eighty-second and Eighty-third Streets, New York (1883, 1886). He also did a large amount of commercial and industrial work, including sugar refineries at Jersey City for Matthiessen & Weichers (1862) and the New Jersey Sugar Refining Company (1867), several important early office buildings, especially those at 62-64 Cedar Street (1876) and 676 Broadway (1873) for the DeLancey Kane estate, and at 67 Wall Street (1871) and the northeast corner of Broadway and Seventeenth Street (1883) for the Daniel Parish estate.
He also designed the bank building once at 52 Wall Street for the New York Life Insurance & Trust Company (1866) and in Jersey City the First National Bank (1860), and was the architect for the Panorama Building on Seventh Avenue and Fifty-fifth Street, New York (1884), altered in 1890 into Tattersall's stables by his son's firm, Lienau & Nash. In addition he designed many other loft buildings, stores, and a few "model" tenement houses. Lienau's practice included considerable educational work as well. Suydam Hall (1871) for the Theological Seminary at New Brunswick, New Jersey, is typical; but finer, because quieter as well as more original, was the Sage Library at the same institution, erected two years later. St. Mary's Hall (1874), Burlington, New Jersey, was also from his drawings. In the South he was the architect of Hodgson Hall (1873) for the Georgia Historical Society at Savannah.
Lienau's architecture was basically eclectic and of its time. Yet it was unusually restrained and is marked always by excellent planning, frankly expressed construction, and satisfactory composition. In the earlier work the influence of the quiet néo-Grec of the Paris he knew was dominant, and this refinement exerted a beneficial effect even on his later work. The row of white marble houses (1869) on Fifth Avenue for Mrs. Colford Jones was dignified, gracious, and sensitively detailed; it had none of the vulgar ostentation current at its time. His work was widely known and admired by his contemporaries; that conscientious critic, Montgomery Schuyler, in his articles for the Architectural Record, chose several examples for especial commendation. His office was known for its thoroughness; both Paul Pelz and Henry Hardenbergh received valuable training there.
Detlef's office was always in New York City, his residence sometimes in New York and sometimes in New Jersey.
He died in New York, where he was then living, after a partial recovery from an attack of typhoid fever.
Detlef Lienau was one of the original fellows of the American Institute of Architects.
Lienau was twice married. His first wife was Catherine Van Giesen Booraem, whom he was married on May 11, 1853. They had three children, J. August (the architect), Detlef Booraem, and Cornelia. After his first wife's death he was married on November 8, 1866, to Harriet Jane Wreaks. There were two children, Eleanor and J. Henry. His son, J. August Lienau was also an architect and for many years a partner of Thomas Nash. They did considerable work for Trinity Church, New York.