Man Chong was from Changyi County (昌邑縣), Shanyang Commandery (山陽郡), which is located northwest of present-day Jinxiang County, Shandong. When he was 17, he served as an Investigator (督郵) in his home commandery. At the time, there was a group of armed thugs led by Li Shuo (李朔) who were causing harm to the locals. After the commandery administrator put Man Chong in charge of dealing with them, Li Shuo surrendered to the authorities and never caused trouble again.
As Man Chong grew older, he became the Prefect (令) of Gaoping County (高平縣; northwest of present-day Weishan County, Shandong). Around the time, an official Zhang Bao (張苞) was abusing his powers by soliciting bribes and causing trouble for the local administration. One day, Man Chong led his guards into the guesthouse where Zhang Bao stayed and arrested him on allegations of corruption. After Zhang Bao died under torture during the interrogation on the same day, Man Chong resigned and went home.
When the warlord Cao Cao held the position of Governor of Yan Province between 191 and 192, he recruited Man Chong to serve as an Assistant Officer (從事) under him. Later, when Cao Cao briefly served as General-in-Chief in 196, he appointed Man Chong as an Assistant in the West Bureau (西曹屬) of his administration. Man Chong was later appointed as the Prefect of Xu County (許縣; present-day Xuchang, Henan), the imperial capital of the Eastern Han dynasty between 196 and 220. During his tenure, Man Chong got into two controversial incidents.
In the first incident, Cao Hong, one of Cao Cao's cousins and trusted generals, had some retainers under him who broke the law while they were in Xu County. After Man Chong arrested and imprisoned the retainers, Cao Hong wrote to him and asked him to release them. When Man Chong ignored his request, Cao Hong brought up the issue to Cao Cao, who summoned the official in charge to come and see him. Man Chong thought that Cao Cao wanted to pardon Cao Hong's retainers, so he immediately executed them. Cao Cao was pleased when he heard about it and he remarked, "Isn't this what an officeholder should do?"
In the second incident, Yang Biao (楊彪), the Grand Commandant, was arrested and imprisoned for allegedly conspiring with Yuan Shu, a warlord who rebelled against the Eastern Han dynasty. Man Chong, who was in charge of interrogating Yang Biao, received requests from his colleagues Xun Yu and Kong Rong to refrain from using torture on Yang Biao during the interrogation. However, Man Chong ignored them and did everything by the book. A few days later, Man Chong reported to Cao Cao: "Yang Biao had nothing to say when I interrogated him. Before executing a criminal, we must first produce evidence of his guilt and show it to the public. Yang Biao is a reputable man. If we execute him without sufficient evidence to show that he is guilty, the people will lose faith in us. I hope you will reconsider your decision carefully and not be too hasty in ordering Yang Biao's execution." Cao Cao then released Yang Biao. Xun Yu and Kong Rong were initially angry with Man Chong when they found out that he tortured Yang Biao during the interrogation. However, they became more amiable towards him after they heard what he told Cao Cao.