Konrad's early life is not well known, but he was described by contemporary church sources as being well educated and highly knowledgeable. It is possible that he received a university education. He was also noted for his strong asceticism and his zeal in defending the church. Much of his early work within the church was related to the suppression of heresy, and he took an active part in the Albigensian Crusade in southern France. Pope Innocent III was one of his early supporters.

Eventually, however, Konrad returned to Germany, the land of his birth. He gradually acquired a position of considerable influence at the court of Ludwig IV, Landgrave of Thuringia. In particular, Konrad gained considerable power over Ludwig's wife, Elisabeth of Hungary, to whom Konrad acted as religious advisor and confessor. In this role, Konrad's treatment of Elisabeth was extremely harsh, and he held her to standards of behaviour which were almost impossible to meet. Among the punishments he is alleged to have ordered were physical beatings and separation from her three children. In 1231, possibly because of Konrad's treatment of her, Elisabeth died.

Konrad also set to work seeking out heresy in both Thuringia and Hesse, and quickly gained a reputation for being unreasonable and unjust. According to most accounts, Konrad accepted almost any accusation as being true, and regarded suspects as guilty until proven innocent. Those accused of being heretics were quickly sought out by Konrad's mobs, and told to repent or else be burnt at the stake. Those accused of heresy were also encouraged to falsely denounce others, with the implication that their life might be spared if they did so. Konrad included commoners, nobles, and priests in his inquisition - Heinrich Minnike, Provost of Goslar, was one of Konrad's first targets, and was burnt at the stake. In 1227, Pope Gregory IX commissioned Konrad to eliminate heresy throughout the whole of Germany, granting him permission to ignore standard church procedure for the investigation of heresy. According to many sources, news that Konrad was to pass through an area almost invariably caused widespread panic.

In 1233, Konrad accused Heinrich II, Count of Sayn, of taking part in "satanic orgies". Heinrich, however, appealed to an assembly of bishops in Mainz, and was declared innocent. Konrad refused to accept the decision, and demanded that the verdict be reversed, but eventually left Mainz to return to Marburg. On the road, he was attacked by several knights, who killed both Konrad and his assistant. The knights may or may not have been in the service of Heinrich.

After Konrad's death, Pope Gregory declared Konrad to have been an upholder of the Christian faith, and ordered his killers punished. Perceptions in Germany, however, was markedly less favourable, and the memory of Konrad was enough to turn opinion against the inquisition for many years.