Kitakyushu City was founded in 1963 when Moji, Kokura, Wakamatsu, Yahata and Tobata Cities merged to become an ordinance-designated city. The former five cities became five wards. In 1974, Kokura-ku was split into north and south while Yahata-ku broke into east and west, making the seven wards we see today. Moji, Kokura and a part of Yahata belonged to Buzen Province, and were the fief of the Kokura Domain in the Edo era. Wakamatsu and most of Yahata belonged to Chikuzen Province, the fief of the Fukuoka Domain.
Kitakyushu has been a transportation hub since ancient times, and was considered an important region by the political powers of each era as a gateway to East Asia. Its development as a city rapidly progressed around the middle of the Meiji era at the end of the 19th century, except for Kokura, the castle town of the Kokura Domain. Railway and port systems were established in order to transport coal mined in the Chikuho area via the port in Kitakyushu.

Using the geographical advantages of Kitakyushu, the Imperial Steel Works were established in Yahata in 1901, centered around Higashida. After that, companies and factories sprung up in rapid succession, and Kitakyushu City supported the industrial development of Japan as one of the country's four major industrial zones.
Due to energy advancements following WW2, coal mines in the Chikuho region were shuttered and steel plants were streamlined. The industrial economy of Kitakyushu slid into decline, and this situation was called "tetsubie" (economic slowdown caused by decreased steel production). The rainbow-colored smoke, which had been seen as a symbol of development as an industrial city, became known as the chief source of air pollution, and pollution became a severe social problem. However, Kitakyushu City went on to overcome the pollution problem and promoted recycling industries. Now the city has a unique presence as an "environmental future city," in addition to being a city of manufacturing. The former site of the steel plant in Higashida now hosts museums of natural and other history, industry, and the environment, and has become a center where the history and culture of Kitakyushu is introduced.