During
World War I, Pavlenko served as the commander of many army units, including a Ukrainian brigade in
Yekaterinoslav. In the spring of 1917, Omelianovych-Pavlenko became an active supporter of the Ukrainian independence movement, and initiated the creation of the
Odessa battalion. He also initiated Ukrainian military academies in
Zhytomyr and
Kamianets-Podilskyi. On 10 December 1918, Pavlenko assumed command of the
Ukrainian Halitska Army, which he led until June 1919. After the union of the UHA and the army of the Ukrainian People's Republic, Pavlenko assumed command of the force. He served as a special attache to Symon Petlura. Omelianovych-Pavlenko commanded the army of the UNR during the
First Winter Campaign (1920). ==Inter-war years==