[1] After the invasion of Yugoslavia during the World War II, Grbić joined the KPJ-led Yugoslav Partisans and became the political commissar of the 2nd Battalion of the 12th Slavonian Proletarian Shock Brigade.
[2] In August 1943, Grbić also became the political commissar of an Anti-Chetnik Battalion established in the Western Slavonia, composed entirely of ethnic Serbs, to fight against the Nazi-collaborating Chetniks in the area.
[2] Grbić held the posts of minister of trade and industry in the government of the Socialist Republic of Croatia, and was member of the central committee of the KPJ, then renamed League of Communists of Yugoslavia (SKJ), and a member of the central committee of the League of Communists of Croatia (SKH).
The federation organised a student strike in which 30,000 students were demanding the expulsion of Grbić, along with Jure Bilić, Dušan Dragosavac, Milutin Baltić [hr], and Ema Derossi-Bjelajac from the SKH, accusing them of opposing the policies of the SKH leaders Savka Dabčević-Kučar and Miko Tripalo.
[2] Historian Sabrina P. Ramet linked the origin of pressure for privatisation of Yugoslav state-owned economy to statements in favour of this process by Grbić in mid-1986.