He was born on December 27, 1566 in Wroclaw (now Poland). However, it came from the old Jesenský family of Horní Jasen (today the village of Turčianske Jaseno in Slovakia), which he claimed to be. He studied philosophy and medicine in Wittenberg and Leipzig, Germany. He continued his studies at the University of Padua, Italy. He was the personal physician of Emperor Rudolf II, head of the chair of anatomy, surgery and medical botany at the University of Wittenberg from 1595 to 1602 and the court physician of the Hungarian King Matthew in Vienna (1608-1612).
From 1613 he worked in Dresden (Germany), Basel (Switzerland), Tiibingen (Germany), Czech Prague and Siena (Italy). 1617-1620. He was the rector of Charles University in Prague. In 1618 he joined politics, was against the election of Ferdinand II. The King of Hungary.
Jessenius came to Prague at the invitation of Danish star Tich Brahe. A professor at the University of Wittenberg, then 34-year-old Jessenius dissected with the permission of Emperor Rudolf II. at a college in Rijeka from Prague University, the body of a man who shoots. This "anatomical theater" began on June 8, 1600 and lasted for five days. On the body of the gallows he demonstrated the shape, size and position of individual organs in the human body. He began autopsy of the abdominal cavity and explained the function of the viscera. He continued through the thoracic cavity, brain, sensory organs and ended up in his limbs. As the man lay on the table, he also cut the sheep's gut to show and compare viewers. About five thousand viewers watched this unconventional "show".
The public was delighted, the Catholic Church was outraged. Jiří Kezelius Bydžovský described him in his Chronicle of Young Boleslave as a person who divides people and eventually settled himself.
The autopsy course and its results summed up Jessenius in a cycle of nine lectures. He published them in Wittenberg, Johannis Jessenii Jessen, Anatomiae Pragae, Anno MDC and solemniter administratatae historia (John Jessenius of Jasene, autopsy history conducted in Prague in 1600).
The autopsy was well received and he reportedly encouraged the reopening of the University of Prague School of Medicine. In the years 1604-1605 Jessenius and his students did other anatomical autopsies that were already part of the teaching (dissection of a woman and a child).
In medical practice, Jan Jessenius emphasized correct diagnosis as the basis for successful treatment. In one of his works he described the determination of disease by color, density and blood clotting. He applied modern surgery. He described in detail the human skeleton and Johannes Kepler based the anatomy of his eyes on the construction of a telescope.
After the battle of White Mountain and the arrival of Ferdinand II. He was arrested and sentenced to death as a leading figure in anti-Habsburg resistance. He was executed on the old town square in Prague on June 21, 1621 (he cut off his tongue, hung his head on the old city tower and exposed his split body in various parts of the city). It is still unknown where John Jessenia's remains are.