Between battles, he was constantly reading scientific publications. In the last months of the war, he was attached to the Topographical Engineer Corps in Tennessee, most likely as a draftsman. When he was discharged, he returned to Chicago.

He had many jobs as an architect from 1865 to 1871, when he formed a partnership with Edward Burling. Eight months after the partnership began, they were inundated with work as a result of the great Chicago fire of 1871. Adler married Dila Kohn in 1872. Kohn was the daughter of Abraham Kohn, who was a pioneer settler in Chicago and a founder of the Kehilath Anshe Ma'ariv Synagogue.

Adler decided to open his own firm in 1879. Soon after he went into business, he hired Louis Sullivan, who was later to become his partner. (The two of them would later build more than 100 buildings, including steel-framed skyscrapers.) The first building Sullivan and Adler designed together was the Borden Block, 1879-1880 at the northwest corner of Randolph and Dearborn Streets (demolished in 1916) Adler's father had the satisfaction of having his son build a new synagogue for his congregation before he died in 1891.

American architect Frank Lloyd Wright went to work for Adler and Sullivan and received his training from them. In 1895, Adler and Sullivan dissolved their partnership. Adler, an expert in acoustics and a pioneer in the development of steel-framed buildings and skyscrapers, was active in professional organizations and wrote many articles on architecture. He died at the age of 56, on April 16, 1900.