Sima Lang was a greatly accomplished political figure of his time. He escaped Luo Yang with his family after Dong Zhuo burned it. He later served Cao Cao. He served first as a regional governor, but soon his compassionate actions earned him the love of the people. Impressed, Cao Cao recalled him to the court, and appointed him as his official assistant. Eventually, he was promoted to the full rank of Governor, and continued to demonstrate his administrative prowess. In spite of all that he had accomplished, he always had words of praise for his younger brother Sima Yi, even saying "I don't even come close to matching his abilities."
It is said that a terrible plague broke out out his soldiers while he was on a campaign with Zang Ba in the year 217. Reportedly, Sima Lang selflessly tended the soldiers who had fallen ill, refusing any medicine for himself. As a result, he fell ill and died.