Pyotr Shchetinkin was born into the peasant family in Ryazan governorate. He studied at a parish school. He worked as a carpenter. In 1906, he was drafted into the army. He served in the 29th Siberian Rifle Regiment (stationed in Achinsk, Yenisei governorate). He graduated from the school of ensigns (1913). Shchetinkin was a participant of World War I and was awarded four St. George’s Crosses for his bravery (1915). He was promoted to Staff Captain (1917).

He wasn’t actively involved in the events of the February and October revolutions of 1917. From the end of 1917, he was the Head of the criminal investigation department of the Achinsk district of the Yenisei governorate, the Head of the operational department of the Achinsk Soviet. Since February 1918, he was a member of the Achinsk District Executive Committee and Head of its military department. Shchetinkin joined the Russian Communist Party (Bolsheviks) – RСP(b) in March 1918 (according to another version, in 1920).

Since the end of May 1918, after the uprising of the Czechoslovak Legion, he was a member of the military revolutionary troika [a commission of three persons to conduct trials and pass sentences in express mode] of Achinsk District Executive Committee and commanded a Red Guard detachment in the battles against anti-Bolshevik forces in Achinsk, Krasnoyarsk, and Minusinsk districts. After the overthrow of Soviet power in Siberia, Shchetinkin hid under the name of Pyotr Eryomin, participated in an underground struggle.

In December 1918, he organized a guerilla detachment in the village of Lapshikha, which fought against the forces of Aleksander Kolchak. In early 1919, Shchetinkin’s guerillas inflicted a series of defeats on the enemy in the Achinsk district and took control of several districts to the north of the railway.

In April, his detachment was encircled by White troops under the command of General Sergei Rozanov and managed to break out. Subsequently, it joined Aleksander Kravchenko’s guerilla army. Shchetinkin’s detachment was transformed into the Severo-Achinsk regiment, and he himself was promoted to Deputy Army Commander and Chief-of-Staff.

During the fighting, the guerillas marched to Minusinsk (September 1919). By the end of autumn, the strength of the army grew to 18-thousand. In January 1920, it joined the 5th Army of the Red Army as the 3rd International Yenisei Rifle Division, Pyotr Shchetinkin became its Chief-of-Staff.

In 1920, he became a member of the Extraordinary Revolutionary Tribunal, which conducted trials of former Kolchak ministers; a member of the Krasnoyarsk governorate Executive Committee; Deputy Chairman of the Achinsk District Executive Committee; a member of the Achinsk and Minusinsk district committees of the RCP(b). He held the position of Commander of the volunteer 21st Siberian Rifle Regiment. The autumn of 1920 saw him, along with his regiment, take part in battles against the troops of General Pyotr Wrangel and in the assault on Perekop. He was a delegate to the 8th All-Russian Congress of Soviets (December 1920).

In 1921, as part of the expeditionary detachment of the Red Army in Mongolia, he participated in battles against the troops of Roman von Ungern-Sternberg and his capture. In 1922–1926, he was Chief-of-Staff of the All-Union State Political Administration (OGPU) of the Siberian Border District. Since 1926, he worked in Mongolia as an instructor of the State Military Guard. Pyotr Shchetinkin was killed in Ulan Bator.