Heftye finished his secondary education in 1878, and took a military education in the following years. From 1880 he worked in the family company Thos. Joh. Heftye & Søn, but in 1885 he returned to the military, enrolling at the Norwegian Military Academy. In 1892 he took education as a telegrapher, and started working in the Norwegian Army engineer department instead of in the infantry. He also became involved in local politics in his native Aker municipality. He belonged to the Liberal Party, and was regarded as being on their radical wing.