Lämmerhirt was born 21 April 1839 in Stolberg (Harz), Kingdom of Prussia (presently Germany), the eldest of six children, to Christian Lämmerhirt, a district court secretary and later vice mayor of Suhl, and Karoline Lisette (née Steher).

He completed the Real school whilst living with a great-uncle in Nordhausen due to the provincial location of his hometown and limited educational possibilities.

He enrolled and studied mechanical engineering at the Karlsruhe Institute of Technology where he belonged to the Fidelitas fraternity.

He then initially was an engineer and later general director for Mülheimer Maschinenfabrik und Eisengießerei (English: Mülheim Machinery Factory and Steel Foundry) which would later become Thyssen & Co. By the end of August 1876, Lämmerhirt relocated his family to Winterthur, Switzerland, where he found employment as general director for the Winterthurer Gusswarenfabrik (English: Winterthur Casting Factory), part of Sulzer Brothers.

Between 1879 and 1883, he was a lead engineer at Bureau Fritz Marti in Winterthur which was involved in building the Gotthard Tunnel (one of his most notable works).