Drafted into the Imperial Russian Army during World War I, Ostashenko served with the Southwestern Front between 1916 and 1917 and was demobilized in early 1918.

After the end of the war, between 1922 and 1923, he was arrested on charges of aiding deserters, but after a suspended sentence was ultimately reinstated in the Red Army.

Ostashenko commanded the 57th Rifle Corps from early 1944 and was made a Hero of the Soviet Union for his leadership of it in two crossings of the Tisza during the Budapest Offensive in October and November.

Ostashenko was born on 19 June 1896 in the village of Bolshaya Lyubshchina, Yanovichskoy volost, Vitebsky Uyezd, Vitebsk Governorate to a peasant family.

In July, he volunteered for the Red Army, serving in the Vitebsky Uyezd military commissariat as a clerk and instructor organizer.

A colonel by December 1937, when he was sent to the Vystrel course, Ostashenko became assistant commander of the 52nd Rifle Division in Mozyr upon graduation in September 1938.

As part of the 28th Rifle Corps of the 4th Army of the Western Front, the 6th fought in defensive battles on the Brest and Bobruisk directions.

[2][3] From December, Ostashenko commanded the 57th Rifle Corps, which served with the 37th and 53rd Armies of the 2nd Ukrainian Front, participating in the attack towards Krivoy Rog.

During the Nikopol–Krivoi Rog, Bereznegovatoye–Snigeryovka, and Odessa Offensives, Ostashenko led the corps in a 350-kilometer advance, crossing the Inhul, the Southern Bug, and the Dniester.

After the corps returned to the 53rd Army, now with the 2nd Ukrainian Front, he led it in the October Budapest Offensive, the capture of Tiraspol, Eger, and settlements and fortified points in Ukraine, Czechoslovakia, and Hungary.

For his "courage and determination" in the Budapest Offensive, Ostashenko was made a Hero of the Soviet Union and awarded the Order of Lenin on 28 April, eight days after a promotion to lieutenant general.