Ghatak's contributions were primarily on stereochemically controlled organic synthesis and he was known developing methodologies for the synthesis of polycarbocyclic diterpenoids and bridged-ring compounds. His work on the four possible racemates of deoxypodocarpic acid, deisopropyl dehydroabietic acid and the corresponding 5-epimers reportedly clarified some of the stereochemical uncertainties existed till then. He demonstrated total synthesis of compounds related to gibberellins, a group of growth-regulating plant hormones. The regio- and stereo-specific intramolecular alkylation rearrangements through diazoketones as well as new annulation reactions involving cationic and radical processes he developed widened the understanding of free radical cyclization chemistry.
Ghatak documented his researches by way of a book, A Century, 1876-1976 and a number of articles published in peer-reviewed journals; ResearchGate, an online article repository, has listed 148 of them. He mentored several doctoral scholars in their researches and his works have been cited by several authors. He was associated with journals such as Indian Journal of Chemistry (Sec B), Proceedings of Indian Academy of Sciences (Chem Sci) and Proceedings of the Indian National Science Academy as a member of their editorial boards and served as a member of the Indian National Science Academy Council from 1994 to 1996.