[3] In 1846 Eidlitz formed a partnership with the German immigrant architect Karl (now Charles) Otto Blesch, who had trained in Munich with Friedrich von Gärtner.

One of their several joint commissions in New York was for St George's Episcopal Church (1846–49), still standing on the west side of Stuyvesant Square.

[7] By that time the design was also influenced by Dr. Stephen Tyng, a new pastor hired for what had become a changing urban congregation, in a neighborhood largely filled with immigrants.

Eidlitz's reputation was marred by his involvement, with H. H. Richardson and Frederick Law Olmsted, in the re-design of the New York State Capitol in Albany.

Eidlitz wrote numerous articles published in such journals as The Crayon in the 1850s and the American Architect and Building News beginning in the 1870s.

Marc converted to Catholicism and kept close ties to the German immigrant community, becoming president of Germania Bank in 1888.

Other evidence suggests he later hid his heritage; his marriage was officiated by the Episcopal priest Tyng, and the Eidlitz children were raised as Christian, according to their mother's tradition.