Takezoe studied Confucian philosophy under Saitan Kinoshita in Kumamoto and soon established his reputation as an able man.
Takezoe went into government service in 1875, where he held several responsible posts till he was posted as consul at Tientsin, North China. He published an account of his travels in Chinese in 1879, describing his meetings with Chinese literati, and enjoyment of the experience of spending time in China, the source and home of great culture.
Though so sympathetic to China, in his official diplomatic work, Takezoe worked to further the interests of his own nation. While Takezoe was stationed at a diplomatic post in Tianjin in 1879-1880, an incident known as the "Ili crisis" occurred in which a Chinese diplomat, Wanyan Chonghou, concluded a treaty with Russia granting Russia far greater concessions than Beijing would have agreed to. Beijing attempted to renounce the treaty and have Wanyan executed. Russia refused to have the treaty renounced, and the other Western powers pressured China to honor its international agreements and to not execute Wanyan. In the end, war was avoided; amidst all of this, Takezoe worked to find a way to take advantage of the situation to Japan's benefit.
He was later transferred from Tianjin to Seoul, where as Ambassador to Korea he played a major role in a plot by Japanese officials to gain some degree of control over the Korean government. The plot failed, Takezoe was physically assaulted, and a number of other Japanese subjects were murdered by Koreans, leading to Foreign Minister Inoue Kaoru leading a mission, alongside Durham Stevens and others, to address these attacks. Takezoe resigned, due to his failure to take proper measures at the outbreak of the Keijo Affair (Seoul Revolt in Korea, 1884), to become a teacher at Tokyo University.
Regarding Chinese politics, he expressed confidence that the Self-Strengthening Movement then underway would successfully lead China out of its difficulties, and back into strength and prosperity.