He started his official career in the state of Cao Wei during the Three Kingdoms period and served in various positions, including Administrator (太守) of Pingyang Commandery (平陽郡) and Agriculture General of the Household of Luoyang (洛陽典農中郎將).
Although Sima Wang was close to Cao Mao, he often felt uneasy in the emperor's presence so he requested to be assigned to positions far away from Luoyang, the imperial capital.
[4] Cao Mao then appointed him as General Who Attacks the West (征西將軍) and granted him imperial authority to oversee military affairs in Yong and Liang provinces on Wei's western border.
After Sima Wang showed up, he strengthened the defences in the region and implemented new defensive strategies which successfully kept the enemy at bay and prevented them from gaining ground.
After his accession, Emperor Wu enfeoffed Sima Wang as the Prince of Yiyang (義陽王), with a princedom comprising 10,000 taxable households, as well as 2,000 troops under his command.
In c.December 268,[6] Shi Ji, a general from the Jin dynasty's rival state Eastern Wu, led troops to invade Jiangxia Commandery (江夏郡).
[7] In 271, the Wu emperor Sun Hao personally led an invasion force to attack Shouchun (壽春; present-day Shou County, Anhui).