In Mannheim Ochsenheimer wrote his first stage comedies (Er soll sich schlagen, Der Brautschatz). At the age of 27 he decided to follow a career as an actor and entered into Quandt's troupe of actors in Bayreuth. His first appearance was on 12 November 1794 as Flickwort in Gotter's Schwarzer Mann. After trying his hand in several fields – he was engaged as an opera tenor for a while – he finally committed himself to acting after successes as Gebhard in Portrait der Mutter and as Fallbring in Dienstpflicht. In 1796 he responded to a call from the Döbbelinsche Bühne (Döbbelin stage) in Stargard. On his way he stayed in Leipzig where he performed at the kürfürstliches Hoftheater (prince-elector's court theatre) as Fallbring and as Stepanoff with the result that he was immediately engaged. So after fulfilling his obligations in Stargard and in Frankfurt/Oder he came to Dresden in early 1797 and became one of the most popular members of an actor company that played alternately in Leipzig and in Dresden. In 1798 symptoms of stress and overstrain began to manifest themselves and his doctor recommended more exercise. Taking long walks in the country Ochsenheimer's interest in lepidopterology was rekindled "and without noticing it he had, in seeking recovery from one task, taken over another, not less laborious one." Around this time he made the acquaintance of playwright Friedrich Treitschke who was returning from Switzerland to Leipzig and who shared both his interest in acting and in lepidopterology. In 1801 Ochsenheimer played Talbot in Schiller's Die Jungfrau von Orleans (The Maid of Orleans) with Schiller attending the performance of 17 September and praising Ochsenheimer's accomplishment. He was now offered guest parts at most major theatres in the German-speaking countries.
In 1802 during a guest performance at the Königliches Hoftheater (royal court theatre) in Berlin he met Jacob Heinrich Laspeyres who encouraged him to publish parts of his entomological journals. Although he went to work immediately he planned the book at such a scale that it was not until 1805 that the first part, the natural history of the butterflies of Saxony, was published. Due to problems with the editor he was forced to discontinue the work and began an even more detailed treatment under the title Die Schmetterlinge von Europa (The Lepidoptera of Europe). In the same year he made a tour to Mannheim and Mainz and also to Frankfurt where he used all his spare time to work in the famous collection of Johann Christian Gerning. In December he was invited to Berlin and again exchanged views and experiences with Laspeyres.
In May 1807 he played twelve guest parts in Wien (Vienna) where Treitschke meanwhile held a position at the k.-k. Hoftheater (imperial-royal court theatre) and would have liked to permanently engage Ochsenheimer. To achieve this Treitschke travelled to Dresden in July and succeeded in negotiating a discontinuation of Ochsenheimer's contract with the Dresden stage. In November 1807 Ochsenheimer came to Wien and that same year the first volume of Die Schmetterlinge von Europa appeared. Although it could be called a greatly enlarged and revised version of the Butterflies of Saxony it did contain many new facts and included several new species which Ochsenheimer had received from Portugal by Hoffmannsegg, found in Viennese collections (from southern France and Russia) and in the Gerning collection. As he was not fully employed from the start in Wien he could complete the second volume (Sphingidae, Zygaenidae, Sesiidae) in 1808. That year Treitsche was forced to cut down on his workload for reasons of health, began to take up lepidopterology again and became Ochsenheimer's companion on many excursions. In 1810 the third volume (larger "macro-moths" including Psychidae) was published. Ochsenheimer purchased the Radda collection, Treitschke bought a small collection, and both were combined. With this basis Ochsenheimer went to work at the next volumes "but from 1815 his powers were waning fast." Volume four was completed, with Treitschke's help, in 1816. It contains supplements to the preceding volumes and a draft system of the noctuid moths (Noctuidae) with many new genera. In 1817 Ochsenheimer was instructed to revise the Lepidoptera collections of the k.-k. Hofmuseum (imperial-royal court museum), a task which took him more than a year as he included all non-European taxa. His health was deteriorating steadily and in the next volume he wrote only part of the first genus (Acronicta); the main work was done by Treitschke. On 23 September 1822 he fainted after a performance in Vienna; on 2 November around 10 p.m. he died.
The following may be an anecdotal generalisation. "After rehearsal he used to leave the city to collect in the vicinity and returned only shortly before the performance. When he had had a lucky day he played marvellously, moving his audience to frenetic applause. But when he had found little or nothing he was disgruntled and did not rise above mediocrity."
As an entomologist Ochsenheimer was one of the most influential lepidopterists of the early 19th century. His work "Die Schmetterlinge von Europa" was later continued by Friedrich Treitschke and grew to ten volumes. Although not accompanied by figures or plates it contains a wealth of information on the biology and ecology of the species and it includes careful and detailed descriptions of new taxa, among them Thymelicus lineola (Hesperiidae), Polyommatus eros, Iolana iolas (Lycaenidae), Psilogaster loti (Lasiocampidae), Hyles zygophylli (Sphingidae), Phalera bucephaloides (Notodontidae), Hoplodrina superstes, Polia serratilinea (Noctuidae), Pyropteron doryliformis, Synanthedon cephiformis (Sesiidae), Pachythelia villosella (Psychidae), Zygaena hilaris, Zygaena punctum, Zygaena angelicae (Zygaenidae) and others.
The Linnean Lepidoptera system had already begun to be subdivided by Fabricius in the late 18th century and Ochsenheimer further refined it by the creation of many new genera. Among them are well-known names like Zerynthia, Charaxes, Endromis, Aglia, Gastropacha, Thyatira, Notodonta, Acronicta, Plusia, Heliothis, Amphipyra, Caradrina, Cosmia, Xanthia, Apamea, Gortyna, Nonagria, Euclidia, Anarta, Mamestra, Polia, Mythimna, Orthosia, Agrotis, Orgyia, Colocasia and others.
Several taxa have been named in Ochsenheimer's honour: the genus Ochsenheimeria Hübner, 1825 (Ypsolophidae) and the species Nemophora ochsenheimerella (Hübner, 1813), Pammene ochsenheimeriana (Lienig & Zeller, 1846) and Pieris ochsenheimeri Staudinger, 1886.