After finishing secondary school in 1950 Mr von Lersner started law studies in Tübingen and Kiel, graduated from the German University of Administrative Sciences Speyer and took his second state examination in law in 1959. He earned a doctorate in the same year under the public law specialist Günter Dürig of Tübingen on the subject of liability for legislative wrongdoing. He then started his career as a lawyer at a number of county halls in southern Baden. A mere two years later von Lersner switched to the federal administration. He worked in the directorate-general 'Social Affairs' at the Federal Ministry of the Interior starting in 1961, later moving to the directorate-general 'Public Security'. It was not until 1970 that he switched to the recently reallocated directorate-general 'Environmental Protection' at the Federal Ministry of Health, where he served as Head of the Directorate 'Water and Waste Management'. In 1973 he was appointed by Minister of Interior Hans-Dietrich Genscher to the office of Head of the Federal Office for Environmental Affairs, the predecessor institution of the UBA
. Mr Lersner served as president of UBA, which was founded in 1974, for 21 years until his retirement in 1995.
Mr von Lersner was above all a generalist in the area of law, stumbling upon environmental protection virtually by accident, as he once said himself in an interview given in 1983. However, it was a chance encounter which became a pet project, to which his tremendous productivity in the area of environmental law attests: between 1970 and 1990 he published more than 50 scientific articles on waste and water legislation and other environmental issues. His management style was rather unorthodox for an agency director of the 1970s and 1980s. As a member of the left wing of the FDP, von Lersner was a strong advocate of the civil liberties of the individual. He saw the UBA as an agency of a new era and took that notion seriously. He took pains to dismantle hierarchical barriers, for example by speaking not only with supervisors but also directly with their subordinates as well – something completely novel at the time. He thought it completely normal to go for lunch in the canteen together with staff. He had an open ear for many people.
It was von Lersner's main objective to establish UBA as an independent agency that could withstand the tides of political change. One story that is still told today is how he managed to establish a B8 pay grade for the UBA's president while he served at the Federal Ministry of the Interior (BMI), thus ensuring that the position did not have the status of political appointee and could therefore not be reassigned after a change of government. He was a staunch defender of staff who were criticised time and again – for example when the superior BMI complained about the "insubordinate style of clothing" at the UBA, or when the scientifically-founded opinions of UBA staff did not coincide with policy expectations within the ministries.
In his private life he had a great interest in history and art. Von Lersner established a tradition of hosting art exhibitions at UBA on a regular basis.