Meng Da originally served Liu Zhang, the Governor of Yi Province (covering present-day Sichuan and Chongqing). He defected to another warlord, Liu Bei, when the latter invaded Yi Province in the early 210s and seized control of the province from Liu Zhang. Liu Bei sent Meng Da to guard Jiangling (), and promoted him to Administrator () of Yidu () later after settling Yi Province. Meng Da's original courtesy name was "Zijing", but he changed it to "Zidu" to avoid naming taboo because "Zijing" was also the courtesy name of Liu Bei's uncle.