He was the minor son of Counsellor-in-chief Tian Ying 田嬰, and inherited the post of his father, as well as his fiefs, Xue 薛 and Teng 滕. He is therefore also known under the name Xue Wen 薛文. Mengchang is his style, not the name of his fief.
With his income, he supported several thousand retainers, among which a lot of so-called wandering knights were to be found, worthy advisors he often relied on. During a travel to the state of Qin 秦 in 299, for example, his retainers helped him to get free after he had been encarcerated in Qin.
A very famous retainer was Feng Xuan 馮諼, who supported his master by "purchasing benevolence" (shi yi 市義) instead of collecting debts. King Min of Qi 齊湣王 (r. 323-284) made him his Counsellor-in-chief, and Lord Mengchang was able to persuade the rulers of Han 韓, Wei 魏, Zhao 趙 and Chu 楚 to unite in an alliance against the common enemy of Qin. Later on he fell into disgrace because of he was wrongly associated with Tian Jia's 田甲 attempted usurpation, and withdrew to his manor in Xue. After some ups and downs the king dispised him so much that he had to flee to the state of Wei, where he was even welcomed as Counsellor-in-chief.
Lord Mengchang took revenge and managed to direct a joint army of Qin, Zhao, Wei and Yan against Qi. Only with the accession of King Xiang of Qi 齊襄王 (r. 283-265) the discrepancies with the crown were cleared. He remained, nevertheless, in Wei, where he eventually died.