Miyoshi was born in Nishi-ku, Osaka as the eldest son in a large family of modest background running a printing business.

While in school, he became friends with short story writer Motojirō Kajii and Nakatani Takao, with whom he published the literary magazine, Aozora (“Blue Skies”), which gave him a venue to publish his poems such as Ubaguruma (“Pram”) and Ishi no ue (“On Stone”), which were favorably received by literary critics, including Hagiwara Sakutaro.

In 1930, Miyoshi brought out his first major anthology of free verse, Sokuryo sen (“The Surveying Ship”).

In 1934 he brought out another anthology, serialized in the literary journal Shiki (“Four Seasons”), together with Hori Tatsuo and Maruyama Kaoru, and became a central figure in the running of the magazine.

Aside from free verse anthologies, such as Nansoshu (“From a Southern Window”) and Rakuda no kobu ni matagatte (“On a Camel's Hump”), which won the Yomiuri Literary Prize, he also wrote literary criticism of verse, Fuei junikagetsu and Takujo no hana (“Flowers on a Table”), a collection of essays, Yoru tantan, and a major critique of fellow poet, Hagiwara Sakutarō.

In the year 2004, the city of Osaka established the Miyoshi Tatsuji Award, for the best outstanding anthology of poetry published nationwide.