Between 1961 and 1967 Paessler studied medicine in Kiel. In 1967 he took his state examination and received his medical licence. From 1967 to 1969 he was assistant physician at the University of Heidelberg’s Krehlklinik and had the chance to work with Prof. Schettler, a pioneer in the domain of arteriosclerosis research. From 1969 to 1970 Paessler completed a one year fellowship in cardiovascular surgery with Prof. Michael E. DeBakey. This was during the era of the first heart transplants and the beginnings of coronary surgery. From 1970 to 1972 Paessler worked as scientific assistant to Prof. Burri in the surgery department at the University of Ulm. Between 1973 and 1977 he was a senior physician in Lindau and in Frankfurt. During this time he also specialised in trauma surgery. From 1978 to 1992 he was chief of surgery and traumatology at the county hospital in Bopfingen.
Since 1986 Paessler is vice president of the Collège Européenne de Traumatologie du Sport (CETS). In 1992 he was visiting lecturer at the University of Pittsburgh (Freddie H. Fu, MD) before becoming chief of the Sportklinik Stuttgart. He held this post until 1993. In the same year he co-founded the European Federation of National Associations of Orthopedic Sports Traumatology (EFOST).
From 1993 onwards Paessler became an attending physician at the Atos Praxisklinik in Heidelberg, where he also held the post of medical director between 1997 and 2000. In 1994 Paessler founded the Georg-Noulis-Fellowship offering young Greek orthopaedic doctors the opportunity to complete a one-year specialised training in knee surgery and sports traumatology. 20 Greek doctors have so far completed the fellowship programme, that was named after the person who originally discovered the Lachman-Test, a test for ligament stability. In the year 2000 Paessler founded an additional fellowship-programme which 14 Chinese doctors have completed so far. In 2001 Paessler was visiting lecturer at the departement of orthopaedic surgery at the University of Ioannina. In 2002 he was visiting lecturer at the Chinese General Hospital PLA Beijing (Prof. Wang, MD). In 2003 he was visiting lecturer at the University of Athens (Prof. Soukacos, MD) and in 2005 at the University of Perugia (Prof. Cerulli, MD). Since 2009 Paessler teaches a bachelor course in physiotherapy at the Berufsakademie Nordhessen, Germany. He is founder of the German internet platforms www.vorsicht-operation.de  and www.medexo.com  that offer patients second medical opinions over the internet.
- 1987 Science Award of the German Association of Trauma Medicine (Deutsche Gesellschaft für Unfallheilkunde): „The Lachman Test for Radiology“( Pässler HH, Maerz S: Der radiologische Lachman-Test. Eine einfache und sichere Methode zum Nachweis von Kreuzbandschäden. Unfallchirurgie 12: 295-300, 1986.)
- 1996 Herodicus Award of the American Society of Orthopaedic Sports Medicine for his publication: Cameron M., Pässler H.H., Vogt M., Thonar E., Evans Ch.H.: The Natural History of the ACL Deficient Knee: Changes in Synovial Fluid Cytokine and Keratin Sulfate Concentrations. Lecture held at the II. World Congress on Sports Trauma / AOSSM 22nd Annual Meeting, Orlando, USA 1996
- Die Chirurgie des vorderen Kreuzbandes (Fischer-Verlag, 1996)ISBN 3-437-21088-2
- Kreuzbandchirurgie (Johann Ambrosius Barth Verlag, 1997)ISBN 3-335-00493-0
- Neue Techniken – Kniechirurgie (Steinkopf-Verlag, Darmstadt, Germany, 2002, (ISBN 3-7985-1227-2) 2. edition in English "New Techniques in Knee Surgery" 2003, Spanish edition 2003, Chinese edition 2004, Russian, Greek und Italian editions in preparation)
- Literature by and about Hans Pässler in the German National Library catalogue
- Literatur von und über Hans Pässler 1. und 2. im Katalog der U.S. National Library of Medicine