Jānis Fabriciuss was born into the family of Latvian farm workers near Ventspils in the Courland Governorate.

[1] He started his military in the Imperial Russian Army in 1900 and served in the Lithuanian Life Guard Regiment.

Fabriciuss joined of the Russian Social Democratic Labour Party in 1903 and in 1904, he was sentenced by the Riga District Court to four years in hard labor with subsequent exile to Yakutia.

Fabriciuss distinguished himself in battles against the German interventionists and rebel formations under the command of Sergei Bulak-Balakhovich.

From August 1919, the head of the Livno-Yeletsk defense region for the campaign against the cavalry of Konstantin Mamontov during his of the southern of the Soviet troops.

From January 1921 he was the chief and military commissar of the 43rd United Courses of the command staff of the Red Army.

The first order was awarded in 1919 "For continuous selfless work at the front in fire", the second, "For distinction in breaking through the defense of the White Poles near Smorgon on 14 July 1920", the third, "for participation in the suppression of the Kronstadt rebellion", the fourth, "for battles in the attack on Warsaw and subsequent rearguard battles "in 1921.