He studied philology at Bonn, obtaining his degree in 1843 with a thesis titled Quaestiones Terentianae. From 1847 to 1849 he was a teacher in Elberfeld, afterwards moving to England, where he taught school in Liverpool until 1863. He returned to Germany as a lecturer at the University of Heidelberg, where in 1873 he was appointed professor. He died in Heidelberg.
Ihne is remembered for the classic Römische Geschichte ("History of Rome"), a work published in eight volumes from 1868 to 1890, and also translated into English. Other works on Roman history by Ihne include:
- Forschungen auf dem Gebiet der rom Verfassungsgeschichte, 1847; later published in English as: "Researches into the History of the Roman Constitution", (1853).
- "Early Rome : from the Foundation of the City to its Destruction by the Gauls" (in English, 1875).
- Zur Ehrenrettung des Kaisers Tiberius (A plea for the Emperor Tiberius), 1892.
- translated Biography @ Meyers Konversations-Lexikon
- History of Rome (at Google Books)
- The Encyclopaedia Britannica Vol XII (Internet Archive)
- Researches into the History of the Roman Constitution in English translation and with an Appendix upon the Roman Knights (1853)
- History of Rome in English (at Internet Archive): five volumes from 1871 onwards: Volume 1 from Aeneas to the Conquest of Italy; Volume 2 covering the Punic Wars; Volume 3 covering from 200 BC to 133 BC; Volume 4 covering Roman institutions and the Gracchi; Volume 5 from the Jugurthine War to Sulla.
- Römische Geschichte in German (also at Internet Archive): remaining three volumes of Roman History covering roughly the period from Sulla's death to the dominance of Octavian / Augustus following the Battle of Actium in 31 BC: Volume 6 and Volumes 7 and 8 combined
- Early Rome : from the Foundation of the City to its Destruction by the Gauls in English translation (1898)
- Early Rome : from the foundation of the city to its destruction by the Gauls HathiTrust Digital Library