Johann Eichinger, who had attended a commercial training school after primary school, served in the Austro-Hungarian army from February to November 1918. After an apprenticeship at the Karl Haas company, a factory for bronze-, gold- and silverware in Vienna's 6th district, he worked at the Main Mint Office in Vienna from 1921. In 1923, the Coin Cabinet of the Kunsthistorisches Museum (KHM) employed him as a technical assistant (auxiliary restorer). There he specialised in the production of galvanoplastics and the conservation of the collection of coining dies. In addition, he handled the official communication (correspondence and services) between the Main Mint Office and the Coin Cabinet. In 1924 he married Maria Fiedler, from whom he was divorced at the end of 1942. After having belonged to the Social Democratic Party from 1922 until it was banned at the end of 1933 and after having been a member of the Vaterländische Front (Patriotic Front), Eichinger applied for membership in the NSDAP in the summer of 1938, which was granted to him on 1 June 1940. When he had to join the Wehrmacht on 29 April 1943, the KHM took his second wife Berta, whom he had married on 28 April 1943, in his place on a temporary basis.

After the end of the Second World War, Johann Eichinger was summoned by the Special Commission of the 1st Instance (for denazification) at the State Office for Popular, Schools, Education and Cultural Affairs because of his NSDAP membership (No. 7,683.918). Senate No. 7, which was responsible for the implementation of the constitutional law of 8 May 1945 banning the NSDAP (Verbotsgesetz) in the Kunsthistorisches Museum and chaired by the First Director August Oktavian Loehr, argued against dismissing Eichinger because he had "never fulfilled a party function in the NSDAP", worked excellently and was "the only expert in his field". Johann Eichinger continued to work in the KHM's Coin Cabinet until his retirement at the end of 1961.