Born in Dortmund (Germany), he did his junior and secondary education in schools run by the SVD in Bad Driburg and Steyl), and joined the order, entering the novitiate in 1925. After completing the first part of his seminary studies, he was assigned to teach in a junior secondary school run by the SVD at St Wendel (Germany) for six months. Subsequently, he was sent to complete his theological studies in Rome (1928-1931), where he was also ordained a priest (1931).
He was appointed a teacher of apologetics at the newly opened SVD Major Seminary at St Augustin near Bonn (Germany). In autumn 1934, he began his ethnological studies in Vienna and became a member of the Anthropos Institute in 1935. He graduated in autumn 1937, defending his thesis Die Urkultur in der kulturhistorischen Ethnologie. Eine grundsätzliche Studie [The primal culture in cultural-historical ethnology. A fundamental study], where he took a critical stand to the views held by Wilhelm Schmidt.
He taught at the SVD Major Seminary St Gabriel in Mödling near Vienna (1935-1939), while doing also some work for the Institute. As W. Schmidt’s interest in results of research of the cultures of the small in stature peoples was still high, Bornemann succumbed to Schmidt’s promptings and agreed to undertake a research among the small in stature peoples in Mindoro (the Philippines). Officially appointed to the Philippines, he left Germany in June 1940 and reached Peking by train via Moscow. Being unable to obtain a visa for the Philippines, because of the strained political situation in East and South-east Asia, he got stuck in Peking for the following six years (1940-1946). Although he felt attracted to the stimulating atmosphere of the Fu Jen University in Peking (at that time run by the SVD), he retained his status as a guest. It seemed to be caused by a number of factors – the SVDs in Peking were not particularly thrilled by a prospect of Bornemann joining them on a permanent basis, he himself seemed not to be too eager to engage in formal duties at the university and stuck to his appointment for the Philippines (although, he did not seem to be too eager to engage in his prospective field research, either). He used the time in Peking doing a library research on his future topic and learning languages (mostly English).
When the Second World War was over, he managed to obtain a visa for the USA and moved there in 1946. He continued his library research on the small in stature peoples in the Philippines, first in Berkeley, then in Chicago and New York.
In 1948, he was appointed to join the members of the Anthropos Institute residing in Chateaux de Froideville near Posieux in Switzerland (canton Fribourg) and eventually, became the editor-in-chief of Anthropos and the successor of Wilhelm Schmidt as the director of Anthropos Institute. His time in Froideville was marred by conflicts with the then almost octogenarian Schmidt. In 1955, Bornemann resigned from his post and moved to St Augustin with the prospect of teaching at the Major Seminary there. In 1958, he moved to Rome and took over the role of an archivist and historian of the SVD. In 1982, he retired and moved back to St Augustin but resigned from his membership in Anthropos Institute.