Kazuhiro Koizumi entered Tokyo National University of Fine Arts and Music in 1969, and received his training in the conducting under Kazuo Yamada. He won the First Place Award at the Second Minon Competition for Conductors in 1970, after which he joined in former Japan Philharmonic Orchestra as an assistant conductor.

In July, 1972, New Japan Philharmonic was founded and engaged him as conductor. In October, the same year, he went to Berlin to further his study in conducting for opera at Hochschule under Professor Rabenstein. He participated in the Tanglewood Music Festival in 1973.

In November, 1973, he won the First Prize at the Third Karajan International Competition for Conductors. As a result, he made his Berlin debut and conducted Berlin Philharmonic.

Maestro Koizumi became the Music Director of the New Japan Philharmonic in January 1975, and remain there till December 1979. By March 1979, he was highly acclaimed in the regular concerts with Berlin Philharmonic, and he continued to dazzle audience and critics throughout Europe.

Outstanding orchestras he had conducted are as follow like, Wiener Philharmoniker, Münchener Philharmoniker, Das Symphonieorchester des Bayerischen Rundfunks, Philharmonica Hungarica, Chicago Symphony Orchestra, Boston Symphony Orchestra, Detroit Symphony Orchestra, Cincinnati Symphony Orchestra, Toronto Symphony Orchestra, and Montreal Symphony Orchestra.

Maestro Koizumi was a Music Director of the Winnipeg Symphony Orchestra in Canada from 1983 to 1984 Season. In addition, he frequently conducted the Royal Philharmonic Orchestra of London and recorded the Tchaikovsky Symphony No. 4, 5 and 6.

After very fruitful collaboration with Century Orchestra Osaka as Principal Conductor, Maestro Koizumi has been appointed as their Music Director from April 2008. And he will be Resident conductor at Tokyo Metropolitan Symphony Orchestra from April 2008 too. Furthermore he has been a Principal Guest Conductor of Sendai Philharmonic orchestra.