In 1972 he graduated from the Leningrad Conservatory in the class of Professor K. N. Nikonchuk. In the same year he began working in the Leningrad Chamber Orchestra of Ancient and Contemporary Music under the direction of N. S. Rabinovich. In 1974 he joined the orchestra of the Leningrad State Academic Maly Opera and Ballet Theater named after V.I. Mussorgsky (Mikhailovsky Theater).
Since 1991, since the founding of the collective, he worked in the Symphony Orchestra of the Capella of St. Petersburg. A year later he returned to the orchestra of the Maly Opera House. From 2007 to the present day, Alexander Kosoyan has been an artist of the Symphony Orchestra of the Capella of St. Petersburg.
Has performed and toured with the ZKR on several occasions with the Academic Symphony Orchestra of the St. Petersburg Philharmonic and the Symphony Orchestra of the Mariinsky Theater. As a member of the Capella Symphony Orchestra, he toured Germany, Switzerland, France, Greece, Holland, Belgium, Spain, Finland and many other countries.
