After joining the Albanian Party of Labour (Alb: Partia e Punes së Shqipërisë) in 1957, he studied in the Soviet Union from 1957 to 1960.

In 1967 he started studying at the Party's School "Vladimir Ilyich Lenin" in Tirana, majoring in Political Economy.

A few months later, in September 1975, he was elevated as member of the Politburo of the Party, as substitute for the recently purged Deputy Prime Minister and Chairman of the State Planning Commission Abdyl Këllezi.

Isai, together with Qirjako Mihali, Pali Miska, and Llambi Gegprifti, represented a new generation of leaders within the Party, which emerged with the termination of relations with the People's Republic of China.

Most recently, he stated that he opposed the command of the First Secretary of the PPSh (Ramiz Alia) who had ordered shooting at protesters in Tirana during the collapse of communism in February 1991.