Though born and raised in Görlitz, Foerster never saw himself a Lusatian and felt the strongest allegiance to Silesia, where he studied since winter term 1861 after a semester at Jena.

Apart from Greek and Roman literature (under Jacob Bernays and Martin Hertz) he studied metrics under Rudolf Westphal, archaeology under August Rossbach, Sanskrit under Adolf Friedrich Stenzler.

In 1875, Foerster accepted a chair at the University of Rostock where he worked as third Professor of Classical Philology besides Ludwig Bachmann and Franz Volkmar Fritzsche.

After acting as Dean of the Faculty of Philosophy in 1879/1880 Foerster went on a research travel to England, Spain, and France (funded by the Prussian Academy of Sciences), where he collated manuscripts and started his third opus magnum, the collection of the orations of Choricius of Gaza which were partly unedited at the time.

In his ceremonial speech he talked about Die klassische Philologie der Gegenwart ("Classical Philology in the Present"), giving his views of the field and of the ideal scientist.

Educated a philologist and humanist, Foerster early turned to archaeology and later to art history; but he never quit pursuing his philological tasks which were his life's work.

During his time in Italy, Foerster was inspired by Rudolf Hercher to collate the manuscripts of the late antique orator and sophist Libanius of Antiochia.

This was a task of major importance for several reasons: Libanius' orations, declamations and progymnasmata had an immense impact on the Byzantine writers because of their admired Attic.

Whilst his historical commentary on the letters and the textual constitution was often criticised by other scholars, Foerster's main achievement remains the most reliable edition of all the works of Libanius.

After a lot of preliminary work (which had considerable impact in the classics) Foerster published his edition of Libanii opera omnia from 1903 until his death, in 12 volumes.