In the circle of Lipps' students he came in contact with Moritz Geiger, Otto Selz, Aloys Fischer and above all Johannes Daubert.
In 1904, Reinach obtained his doctorate in philosophy under Lipps with his work Über den Ursachenbegriff im geltenden Strafrecht (On the concept of cause in penal law).
He attended several lectures and seminars on penal law by the legal theorist Ernst Beling, by which he was quite impressed and to which he owes a great deal of inspiration of his later works.
On his turn Reinach appears to have inspired several young phenomenologists (like Wilhelm Schapp, Dietrich von Hildebrand, Alexandre Koyré and Edith Stein) with his lectures.
Moreover, in 1912 Reinach, together with Moritz Geiger and Alexander Pfänder founded the famous Jahrbuch für Philosophie und phänomenologische Forschung, with Husserl as main editor.
Besides his work in the area of phenomenology and philosophy in general, Reinach is credited for the development of a forerunner to the theory of speech acts by Austin and Searle: Die apriorischen Grundlagen des bürgerlichen Rechtes (The A Priori Foundations of Civil Law) is a systematic treatment of social acts as performative utterances and a priori foundations of civil law.
Reinach had said shortly before his death that he would only teach philosophy in the future as a means of leading men to God, and this may have been reflected in these writings.