Born in Berlin, Heintzman worked in various manufacturing jobs as a youth, eventually settling in at a German piano factory.

It is believed by the Heintzman family that Theodor immigrated on the same boat as Heinrich Engelhard Steinweg, another piano-maker, and the two attempted to start a business in New York City.

They soon parted ways, however, with Heintzman taking his family to Buffalo where he started again; Steinweg eventually changed his name to Steinway and became a successful piano manufacturer in his own right.

From 1858 to 1860 Heintzman ran Western Pianoforte Manufactory Company in Hamilton, Canada West (founded in 1856 by Charles Thomas).

A property developer's plan to tear it down in the early 1980s sparked a protest from local citizens, and a compromise was reached wherein the exterior has been restored in the original Queen Anne Revival style.