Denys Prokopenko is a descendant of ethnic Karelians. His grandfather returned alive from the Soviet-Finnish (Winter) War of 1939-1940.

He graduated from the Faculty of Germanic Philology of the Kyiv National Linguistic University with a degree in English. At the same time, he was involved in sports. One of the active fans (ultras) of the "white and blue" football club Dynamo (Kyiv). He is married to Kateryna Prokopenko.

From 11 July 2014, he took part in the anti-terrorist operation in eastern Ukraine as part of the Azov. In Azov, he demonstrated leadership qualities and became a platoon, company, and later battalion commander. In July 2017, he was appointed commander of the Azov Special Forces detachment. He became the youngest commander in the history of the Armed Forces and the National Guard.

Russian invasion of Ukraine (2022)
On 24 February 2022, Azov, under the command of Denys Prokopenko, took over the defence of Mariupol and nearby villages. On 7 March, during the Russian invasion of Ukraine, Denys Prokopenko called for the skies over Ukraine to be closed to prevent a humanitarian collapse in Mariupol, as "the enemy is violating the rules of war by shelling civilians and destroying the city's infrastructure, and subjecting Mariupol residents to genocide".

On 19 March, President of Ukraine Volodymyr Zelenskyy awarded the title of Hero of Ukraine to the commanders of the units that continued the defence of Mariupol, Denys Prokopenko and the commander of the 36th Marine Brigade, Volodymyr Baranyuk.

On 18 April, the blockade of Azovstal began. Denis became the voice of the Azov regiment and regularly recorded videos about the situation at the plant.

On 4 May, the commander of the Azov regiment, Prokopenko, said that the Russian military had managed to break through to the territory of Azovstal, but the garrison continued to follow orders to hold the line.

On 8 May, he gave an interview to Ukrayinska Pravda from the besieged Azovstal, where he criticised the actions of the military defending the line of demarcation with Crimea.

On 20 May, he said that on the 86th day of the circular defence of Mariupol, he received an order from the highest military command to save the lives and health of the garrison's soldiers and to stop defending the city. The priority requirements for the evacuation of civilians, the wounded and the dead were met.

Initially, all the prisoners were held in Olenivka. A few days later, Denys Prokopenko and the entire command staff of the Mariupol defenders were taken to Moscow, probably to Lefortovo.

On 21 September 2022, he was released from captivity as a result of a prisoner exchange[18][19]. He was interned in Turkey together with the commanders of the Mariupol defenders: Svyatoslav Palamar, Oleh Khomenko, Serhii Volynskyi, Denys Shleha.

On 8 July 2023, he returned to the territory of Ukraine.