Fabiani was born to father Antonio Fabiani, a Friulian latifondist from Paularo of Bergamasque ancestry, and mother Charlotte von Kofler, a Triestine aristocrat of Tyrolean origin.
On 15 May 1921 - less than a year after the burning of the Slovenian National Hall in Trieste, which he had designed-Fabiani became a member of the Italian fascist movement.