He hailed from Xiangxiang 湘鄉 (modern Shuangfeng 雙峰, Hunan) and obtained the academic jinshi degree in 1838. He entered the Hanlin Academy 翰林院 and became a secretary (sheren 舍人) of Mujangga 穆彰阿 (1782-1856), a member of the State Council (junjichu 軍機處).
In 1843, he was sent out as an examining editor (jiantaoguan 檢討官) to oversee the provincial examinations of Sichuan and therefore rose to the official rank of reader-in-waiting (shidu 侍讀). He rose the ladder of official career by the offices of academician of the Grand Secretariat (neige xueshi 内閣學士) and vice minister (shilang 侍郎) of several ministries in sequence.
Zeng Guofan was influenced by thinkers of his own period that stressed the importance of adapting Neo-Confucian state philosophy to the circumstances of the modern world, the so-called "school of facts" (shixue 實學).
In 1852, the Taiping Rebellion (Taiping qiyi 太平起義, 1851-1864), originating in Guangxi, spread towards Zeng Guofang's home province Hunan. He obtained the imperial order to return home and to organize local resistance against the Taiping rebels, together with the governor (xunfu 巡撫) of the province. Zeng Guofan answered this imperial edict with the suggestion not to use the normal Green Standard troops (lüyingbing 綠營兵) but, according to the method of the late Ming period 明 (1368-1644) war historian Qi Jiguang 戚繼光 (1528-1588), to recruit soldiers from among the population and to train them.
The Emperor accepted this proposal, and Zeng Guofan so founded the new army (xinjun 新軍) of the "Hunan braves" (Xiangyong 湘勇), also called the "Hunan army" (Xiangjun 湘軍). In 1854, the new army was ready for battle, consisting of more than 17,000 troops of naval and infantry units. In the first battles at Yuezhou 岳州 (modern Yueyang 岳陽, Hunan) and Jinggang 靖港, the new army was defeated by the Taiping rebels. Zeng Guofan could not stand the shame and wanted to drown himself, but he was held back by his staff.
He then started refining the training and was then able to occupy Yueyang. In October 1854, the Hunan Army even could liberate Wuchang 武昌 (modern Wuhan 武漢), the capital of Hubei. The emperor rewarded him with the office of governor of Hubei, but soon again took him away this post, in fear of Zeng's growing military and political strength.
Yet Zeng continued to lead the Hunan Army against the Taiping rebels, but only held the vain brevet title of vice minister. In early 1855, his army attacked Jiujiang 九江 and Hukou 湖口, Jiangxi, but was repelled and withdrew to Nanchang 南昌 (the capital of Jiangxi). This defeat had no greater disadvantages for Zeng Guofan as he had already won high reputation not only in Hunan, but also throughout the empire and was supported by the local governments wherever his army came to.
In March 1853, he had to leave command because his father had died. Hu Linyi 胡林翼 (1812-1861) took over the command of the Hunan army and continued the fight against the Taiping rebels.
In June 1858, Zeng Guofan was prematurely entrusted with the fight against the Taiping troops in the province of Zhejiang and was ordered to oversee the fights in Fujian and in Sichuan the territory of which was invaded by the Taiping general Shi Dakai 石達開 (1831-1863). Yet Zeng Guofan suggested a better strategy against the Taiping by encircling their "Celestial Capital" (Tianjing 天京) that had been set up in Nanjing 南京, Jiangsu. He cut off their logistics in Wuhu 蕪湖, Jiangsu, and first advanced against the Taiping troops in the province of Anhui.
In early 1860, the traditional Qing army was utterly defeated by the Taiping. This catastrophy caused the Qing court to endow Zeng Guofan with the brevet title of Minister of War (bingbu shangshu 兵部尚書) and to appoint him to the post of governor-general (zongdu 總督) of Liang-Jiang 兩江, with the title of Grand Minister Inspector-General (qinchai dachen 欽差大臣).
In Sepember 1861, he organized the conquest of Anqing 安慶, Anhui, that was conducted by his younger brother Zeng Guoquan 曾國荃 (1824-1890). In November, Zeng Guofan was granted the title of Junior Guardian of the Heir Apparent (taizi shaobao 太子少保, see Three Dukes) and was allowed to take over the highest command of the provinces of Jiangsu, Anhui, Jiangxi and Zhejiang.
Zeng Guofan suggested that Zuo Zongtang 左宗棠 (1812-1885) be appointed commander-in-chief of Zhejiang and Li Hongzhang 李鴻章 (1823-1901) governor of Jiangsu. Zeng Guoquan then advanced from Anqing towards the Celestial Capital, and Zuo Zongtang from Jiangxi towards Zhejiang. Li Hongzhang, whose troops were assembled to protect the merchant city of Shanghai, was to advance towards southern Jiangsu. In October 1862, the Celestial Capital was encircled, yet the siege was only ended with the assault on the city in July 1864.
Zeng Guofan was highly rewarded and granted the title of 1st-class Marquis (yideng yiyong hou 一等毅勇侯) and bestowed the title of Grand Mentor of the Heir Apparent (taizi taifu 太子太傅). He was furthermore allowed to wear a double-eye peacock feather, which was a very prestigious decoration.
As an experienced military commander, he was entrusted with the suppression of the Nian rebellion (Nianjun qiyi 捻軍起義, 1851-1868) in May 1865 and took over command of the armies in the provinces of Zhili 直隸 (modern Hebei), Shandong and Henan. All his efforts did not result in a defeat, and so the next year he was replaced by Li Hongzhang, while Zeng Guofan himself was sent back to the post of governor-general of Liang-Jiang.
In 1867, he was appointed governor-general of Zhili. In June 1870 he solved the case XXX of the French missionaries in Tianjin. In September he was sent back to Liang-Jiang.
Zeng Guofan had seen that the superior firepower of the Western countries enabled them to win virtually all battles against the less well equipped Chinese troops of all kind. He therefore started a programme of self-strengthening (later called self-strengthening movement, ziqiang yundong 自強運動), used foreign cannon for his campaigns and stressed the importance of first buying and then learning how to produce cannon and to build ships.
In 1863, Zeng Guofan had the first Chinese steamship built, the "Yellow Swan" (Huanghu 黃鵠) and sent out Rong Hong 容閎 (Yung Wing, 1828-1912) to America to buy machines and weapons. In 1866, Zeng inaugurated the first Chinese factory for military equipment, the Jiangnan Arsenal (Jiangnan chuangzao zongju 江南創造總局) in Shanghai, together with Li Hongzhang. Rong Hong was only the first of a large series of students that Zeng Guofang sent to the USA. Many of them would eventually be the founders of China's first industrial companies.
As a governor-general, Zeng Guofan displayed great responsibility for China's "grainhouse" and independently exerted a Confucian-style government, as he had learned during his education. He was known for his uprightness, the sincerity with which he treated his staff, for his incorruptibility and his austerity. He made systematic and well-founded use of the law, saw the peasantry as the most important base of the empire and therefore lowered taxes in regions inflicted by war. After the defeat of the Taiping, he took great care for the reconstruction of the whole region of the southeast and established schools and academies for the education of future state officials.
Zeng Guofan died in March 1872 in Nanjing. He was granted the posthumous title of Duke Wenzheng 文正公, the "Cultivated and Upright". His collected writings were published in the collection Zeng Wenzhenggong quanji 曾文正公全集. Another publication, Zeng Wenzhenggong shoushu riji 曾文正公手書日記, is a facsimile of his hand-written diary.