Born in Kiev into a family of Belarusian landed gentry, Vannovsky chose his career early on in his life and began military schooling.

During the Russo-Turkish War of 1877–1878, he took the prominent role as the chief of staff of the Ruschuk Detachment, under the Tsesarevich, future emperor Alexander III.

Vannovsky was one of the most successful Minister of War during the course of the Russian Empire, he was in office during most of the reign of Emperor Alexander III and the early reign of Emperor Nicholas II from 1881 to 1898, he was credited with maintaining order, preventing corruption and reforming the Russian military during his role as the Minister of War.

And Pyotr, followed to the Vannovsky Family tradition to choose his future career at a young age, he chose to serve in the military and was strongly supported by his father.

Later for military distinction, he was awarded the Order of St. Vladimir of the 4th degree with swords and a bow, and was subsequently appointed the commander of his own regiment.

After hostility ended in 1857, he became the head of several military schools, and thanks to his efforts, many infantry officers had been trained to take up the post of small unit commander and managing weapons, and those who graduated in the first category was granted the next rank ahead of the schedule.

At the beginning of the Russo-Turkish War, he commanded the 12th Army Corps to crossed the Danube, the Army Corps was later incorporated into the Ruschuk Detachment (the Eastern Detachment), for which he was appointed chief of staff of it, commanded by the tsesarevich, the future emperor Alexander III, whom he would become close friend with after the war.

On 14 November, Suleiman Pasha with his men tried strike the Russian Army rear once again, and a decisive battle took place between the Bulgarian villages of Trastenik and Mechka.

During the battle, the Ottomans, having superiority in manpower and artilleries, went on an offensive, inflicting the main blow at the right flank of the Russian Army.

Further unravelling revealed that the Ottomans planned to play defensive against the left and center of the Russians, and concentrate the troops to strike on the right flank of them.

The battle developed well for the Russians, later with the support of the 2nd Brigade of the 35th Infantry Division, a Ukrainian Regiment and reinforced by the cavalry of Freiherr von Driesen [ru], the Ruschuk Detachment advanced and launched an attack on the left flank of the Ottomans.

For five months the troops of the Ruschuk detachment, under the command and leadership of the heir to the Russian throne and then the emperor of the great Russia Alexander III, stood almost unceasing battles and battles with the enemy, constantly exceeding their number (sometimes several times), which had the benefits of an offensive course of action, on strong fortresses, having good routes of communication and being led to be considered the best of Turkish commanders.

This task was accomplished brilliantly, despite the difficulties stemming from the need to detain, for a long time, the vastly superior forces of the enemy, constantly making attempts to break through our defensive lines.Later, the Ruschuk Detachment was tasked with interrupting the Ottoman communication line between Ruse and Shumen, in order to capture Silistra.

After the battle, Grand Duke Nicholas Nikolaevich offered the Tsesarevich to go on a vacation, he refused and was accepted by the Grand Duke, this would eventually contribute to the development of the successful career of Vannovsky: Vannovsky's detachment was the first in Russian military history to receive biscuits as food, rather than having bread, to reduce the possibility of getting gastrointestinal disease.

The Anarchist Peter Kropotkin opined that, "A military officer had thus to interfere for the defense of the students against the Ministry of Public Instruction.