He is a Persian language professor in Netherlands. He a chair of Persian language and literature and the cultural history of Iran at Leiden University. His special fields of interests is Shia and Sufi in Islam.
On 15 May 1998, Dr J.G.J. Ter Haar (1941) delivered his inaugural speech as Professor of Persian Language and Literature and the Cultural History of Iran. The speech was entitled: In De Stilte Van De Sharia, Een debat over de islam in het moderne Iran (In the Silence of the Sharia; a debate on Islam in Modern Iran).