He was employed by the Nakajima Aircraft Company, but lost his job with the prohibition on military industries in Japan after World War II.

He sent the second draft of his first detective story, The Tattoo Murder Case, to the great mystery writer Edogawa Ranpo, who recognized his skill and who recommended it to a publisher.

Takagi was a self-taught legal expert and the heroes in most of his books were usually prosecutors or police detectives, although the protagonist in his first stories was Kyosuke Kamizu, an assistant professor at Tokyo University.

A subsequent stock market crash means that he has no hope of returning to his old career and therefore he accepts a job from an old friend even though he eventually discovers that the new firm he works for is really an agency for industrial espionage.

Takagi came into contact with the Tokyo tattoo scene while writing his first novel (Shisei Satsujin Jiken, 1948) and began to document it.