[5] His father worked as a clerk in the Burma Railways, where he had sought employment during the British Raj.

Karat studied at the Madras Christian College Higher Secondary School[7] in Chennai.

[8] Encouraged by the Scottish theologian Duncan B. Forrester, one of his college professors, he got a scholarship to Britain's University of Edinburgh, for a master's degree in politics.

In 1970 he received an MSc degree from the University of Edinburgh for the thesis "Language and politics in modern India".

At Edinburgh he became active in student politics and met Professor Victor Kiernan, the well-known Marxist historian.

Karat was one of the founders of the Students Federation of India (SFI), in Jawaharlal Nehru University.

During this period his associates included N. Ram, later editor of The Hindu daily, the radical women's activist Mythili Sivaraman and, less closely, P. Chidambaram, who later became India's finance minister.

During his era the Communist Part of India (Marxist) saw a sharp downfall due to his rigid behaviour on party line.