Alongside Adelard of Bath, John of Seville, Gerard of Cremona and Plato of Tivoli, Herman is the most important translator of Arabic astronomical works in 12th century.

[9] In his own account, he was born in the early 12th century, possibly around 1105 or 1110, in central Istria, then part of the Duchy of Carinthia in the Holy Roman Empire.

[10] The location is difficult to pin down given the much broader extent of the March of Istria in the 12th century, which included the Karst Plateau, Trieste, Duino and most of the area of later Inner Carniola, possibly even encompassing the upper Vipava Valley.

[9] Richard Hakluyt, quoting an anonymous Latin source from the time of the Second Crusade, says that Robert "traveled through France, Italy, Dalmatia, and Greece, and came at last into Asia, where he lived in great danger of his life among the cruel Saracens, but yet learned perfectly the Arabian tongue" and "returned by sea into Spain", adding that Herman "had accompanied him in his long voyage.

Despite being an imperfect translation, Lex Mahumet pseudoprophete remained the standard one for centuries, circulating in manuscript before being printed in the 1543 edition published in Basel by Theodor Bibliander.

Herman's first known translation was the sixth book of an astrological treatise Liber sextus astronomie by the Jewish writer Sahl ibn Bishr.

Circa 1140 Herman translated into Latin the astronomical work of Abu Ma'shar al-Balkhi Kitab al-madkhal ila ilm ahkam al nujum (Introduction to Astronomy).

Herman's less literal translation was published several times under the title Liber introductorius in astronomiam Albumasaris, Abalachii (Augusta Vindelicorum, Augsburg 1489; Venice 1495 and 1506).

Charles Burnett (2001) postulates that Herman collaborated with Robert of Ketton and Hugo of Santalla on the Liber novem iudicum (the Book of Nine Judges), a collection of translations of Arabic astrologers, notably al-Kindi.

Some other works are believed to be Herman's: In the text (or a manuscript, the syntax of this article was not clear) of De indagatione cordis there are many names of scientists and scholars whose work Herman knew and used: Abu Ma'shar al-Balkhi (787–886), Sahl ibn Bishr, Aomar Tiberia, Abu al-Kindi (801–873), the eighth-century Jewish astrologer Al Batrig Mashallah (Messahalla), Hermes, and Dorotheos of Sidon.