Born June 9, 1967 in Chiba Prefecture, he made his manga debut with Shueisha in 1987 with the one shot Bakuhatsu! Yuriko-sensei (爆発！ ゆりこ先生, Explode! Yuriko-sensei) In 1988, the one shot AT Lady! won the 28th Akatsuka Award for best comedic story (under the name Takeshi Nomura のむら剛), leading to a series in 1989 in Weekly Shonen Jump, Shueisha's main weekly shonen magazine. After that series quickly ended, he soon met mangaka writer Shou Makura (Makura Shou, 真倉翔) and together, they began working on the series that would eventually become both of their greatest efforts: Hell Teacher Nūbē (Jigoku Sensei Nube, 地獄先生ぬ～べ～). After two one-shots under the name Jigoku Sensei Nubo (one in the 1992 Autumn Jump Special, another appearing in the main magazine early in 1993), the series began serialization in Jump Issue 38 in 1993 and had a successful 6-year run through Issue 24, 1999. The manga eventually ran for 276 chapters over 31 volumes, as well as a 49 episode anime series by Toei Animation (from 1996 to 1997), as well as notoriety from one magazine as being one of the "Five Best Big Breast Manga". (due to the slightly-ecchi characters created by Makura and drawn by Okano)
After Nube ended, Makura and Okano worked together on another Jump manga in 2000, Tsurikkies Pintarou (ツリッキーズ ピン太郎), a manga about a boy who's the descendant of a legendary fisherman. This series, though, did not last too long and broke apart the Okano/Makura team. After breaking with Makura, Takeshi Okano came back in 2001 with Magician² (魔術師2), but this series too did not last too long.
In 2004, Takeshi Okano returned to the strange and peculiar with Gedou the Unidentified Mysterious Boy (未確認少年ゲドー Mikakunin Shounen Gedou). This series was an interactive study in cryptozoology similar to how Nube was a study in the supernatural. While lasting longer than his two previous efforts in manga with 47 chapters and 5 manga volumes, the series could not keep the interest of fickle Jump readers for too long and ended one year after it started.
In 2005, Takeshi Okano joined in on another collaborative effort for an extremely well known and popular series. Digimon, the popular monster partner series, was making a slight resurgence in the public eye, coinciding with a new anime series, (Digimon Savers, which began in April, 2006), and the start of the new manga series Digimon Next in the pages of Shueisha's video game magazine, V-Jump. Okano is the artist on this project, working alongside Tatsuya Hamazaki (Hamazaki Tatsuya, 浜崎達也), writer known for the manga version of .hack//Legend of the Twilight and novelization for Jump properties such as Saint Seiya and One Piece. Like before, Okano finds himself in a collaborative effort regarding children facing extraordinary circumstances.
In 2007, Okano and former partner Shou Makura finally reteamed to create a new series based on Hell Teacher Nube character Izuna Hatsuki.