Kapustiansky was born in Yekaterinoslav Governorate (in present-day Dnipropetrovsk Oblast) in central Ukraine, then part of the Russian Empire.

Kapustiansky was a founder of the Organization of Ukrainian Nationalists and a member of its Provid, or Directorate, from 1929 until his death in 1969.

During World War II, he cooperated with the Nazis and tried to establish a Ukrainian section in the Wehrmacht.

[3] After the war, he settled in Munich and became the first chief of the military section of the Government-in-exile of the Ukrainian National Republic.

He wrote Pokhid ukraïns’kykh armii na Kyïv–Odesu v 1919 rotsi (The March of Ukrainian Armies on Kiev–Odessa in 1919; 1922, 2nd edn 1946) and numerous articles on military affairs.