In February 1919 he succeeded Denisov as Commander of the Don Army, within the Armed Forces of South Russia.

On 18 April 1920, shortly after his arrival from Novorossiysk to Evpatoria in the Crimea, he was brought to trial along with Lieutenant-General Kelchevsky, chief of staff of the Don Army.

General Sidorin was appointed Governor of Sevastopol (Russia) but emigrated from the Crimea one month later in May 1920 and went into exile: first in Bulgaria, then Serbia, then Czechoslovakia in 1924 and finally in Germany in 1939.

Under the title "The tragedy of the Cossacks", these articles were published in a separate book in four parts in 1936-1938 in Paris (without mentioning the names of the authors).

He died in Berlin on 20 May 1943 and was buried in the Berlin-Tegel Russian Orthodox Cemetery (4th quarter, 12th row, grave No.