He studied medicine in Prague and Strassburg, earning his doctorate at Prague in 1878.
In 1889 he described the disease Anaemia leucaemica infantum, a chronic anemic disease that affects children under three years of age, which was named "Jaksch"s anemia" for him. Following graduation he remained in Prague as an assistant to pathologist Edwin Klebs (1834-1914). From 1879 to 1881 he worked with his father, and in 1881-1882 was an assistant to Alfred Pribram (1841–1912).
In 1882 he moved to Vienna, where he was assistant to Hermann Nothnagel (1841-1905).
The following year he received his habilitation in internal medicine. In 1887 he was appointed professor of pediatrics at the University of Graz, later becoming a professor of internal medicine and director of the second internal clinic at Karl-Ferdinands Universität (German University) in Prague.
Here, he was instrumental in the construction of a modern clinic that first opened in 1899. He worked in Prague until his retirement in 1925.
He was a prolific author, one of his better efforts being Klinische Diagnostik innerer Krankheiten (1882), a work that was published over several editions and later translated into English.
On his initiative he started with the construction of a new, much more modern and hygienic designed clinic that was opened in 1899. Jaksch was awarded in 1899 for this construction of his permanent bathrooms at the nursing exhibition in Berlin. In 1882 von Jaksch married Adele von Haerdtl (1867−1944) in Vienna.
He had one brother named August Jaksch von Wartenhorst (Prague 2 jan 1859 - Klagenfurt 3 jan 1939).
In urine Jaksch discovered Acetoacetic acid, a melanin probe and manganese toxicosis. He also discovered new diseases such as Von Jaksch"s disease (he himself named it anemia pseudoleukaemica infantum).
In 1923 he was the first one who discovered the autoimmune disease Relapsing polychondritis, that he himself named Polychondropathia.
German Academy of Sciences Leopoldina]
He was widely honored and awarded, and an including member of the Leopoldin-Karolin, and the German Academy of natural scientists in Halle and the medical surgical Academy in Perugia.