Cai Mao came from the elite Cai family in
Xiangyang,
Nan Commandery (), the capital of
Jing Province (covering present-day
Hubei and
Hunan). His father was Cai Feng (). His aunt (Cai Feng's sister) married
Zhang Wen, who served as the Grand Commandant () during the reign of
Emperor Ling. Cai Mao had two sisters – one married
Huang Chengyan while the other married
Liu Biao. Cai Mao also had two other notable relatives: Cai Zan (), courtesy name Maogui (), who served as the Chancellor of Mei (); and Cai Yan (), courtesy name Wengui (), who served as the Administrator of Ba Commandery (). The Cai family would later be robbed and massacred by bandits during the Yongjia era (307–313) of the reign of
Emperor Huai of the
Jin dynasty (266–420). Cai Mao was known for being arrogant and proud. He served as a military officer under his brother-in-law
Liu Biao, the Governor of
Jing Province. In 190, when Liu Biao first started his tenure in Jing Province, Cai Mao, along with
Kuai Liang and
Kuai Yue, assisted him in quelling local rebellions and consolidating control over the province. Cai Mao subsequently served as the Administrator () of various
commanderies in Jing Province, including Jiangxia (), Nan Commandery () and Zhangling (). In 192, after Liu Biao received the honorary appointment of General Who Guards the South () from the Han imperial court, he appointed Cai Mao as his military strategist. Liu Biao had two sons –
Liu Qi and
Liu Cong – born to his first wife. The younger one, Liu Cong, married a niece of Cai Mao's sister
Lady Cai, so the Cai family favoured him and wanted him to succeed Liu Biao as the Governor of Jing Province in the future even though Liu Qi, being the elder son, should be the rightful successor. In 208, Cai Mao and Liu Biao's maternal nephew Zhang Yun () plotted to harm Liu Qi. When Liu Qi heard about it, he found an excuse to leave Xiangyang and be the Administrator of
Jiangxia Commandery. After Liu Biao's death later that year, Liu Cong became the new Governor of Jing Province with support from the Cai family. In late 208, when the warlord
Cao Cao, who controlled the Han central government and the figurehead
Emperor Xian, led an army south to attack Jing Province, Cai Mao, Kuai Yue, Zhang Yun and others managed to persuade Liu Cong to surrender to Cao Cao. As Cai Mao had known Cao Cao since their younger days, Cao Cao treated him well and even visited his home. From then on, Cai Mao served under Cao Cao and subsequently held the following positions in Cao Cao's administration: Assistant Officer of the Household (), Major () and Changshui Colonel (). He was also enfeoffed as the Marquis of Hanyang Village (). ==In
Romance of the Three Kingdoms==