After finishing his medical studies he practiced ophthalmology in Munich. He is remembered for his research in the field of parapsychology. He was inspired by the British Society for Psychical Research, and with philosopher Traugott Konstantin Oesterreich (1880-1949) tried to establish a similar institute in Germany.
With Albert von Schrenck-Notzing (1862-1929), he fought for the recognition of parapsychology as a serious subject of study.
Among his most important contributions to the field of parapsychology were his experiments in clairvoyance, conducted at a time when most such research concerned telepathy. These experiments involved selected participants in identifying the targets – typically, text or drawings – concealed in opaque envelopes, while (unlike a telepathy experiment) no persons were aware of the contents of the envelope.
Tischner"s monograph Telepathie und Hellsehen (1921) collected his reports on these studies. In this work, Tischner referred to telepathy and clairvoyance as instances of a more general faculty of Außersinnlicher Wahrnehmung, thus, in its translation, coining the term extrasensory perception.
Tischner performed research on the possibilities of merging homeopathy with evidence-based medicine, and published a book on the evolution of homeopathy named "Das Werden der Homöopathie".
He was the author of works on homeopath Samuel Hahnemann, titled "Samuel Hahnemann"s Leben und Lehre" and "Die Bildwerke Hahnemanns und ihre Schöpfer". In the field of hypnosis he produced writings on the life and work of Franz Anton Mesmer, called "Franz Anton Mesmer, Leben, Werk und Wirkung" and "Mesmer und sein Problem, Magnetismus, Suggestion, Hypnose".