Apicomplexan phylum comprises obligate intracellular parasites, infecting a wide range of hosts from vertebrates to invertebrates. My thesis covers two main aspects of their biology. Firstly, I delineated the establishment of intracellular parasitism in Apicomplexans over the course of evolution by studying the phylogeny, morphology, metabolic and invasive capabilities of a fish coccidian parasite, Goussia janae. In the second section of the thesis, I dealt with the investigation of the role of two post-translational modifications, proteolytic processing and palmitoylation, of proteins. We identified and characterized the essentiality of an aspartyl protease 3 (TgASP3) for the lytic cycle of the parasite by highlighting its role as a maturase for integral secretory organelle proteins. Furthermore, we identified a potential drug candidate 49c, a peptidomimetic inhibitor that targets. We characterized the essential nature of 2 inner membrane complex (IMC)-resident palmitoyl acyl transferases, TgDHHC2 and TgDHHC14, and a Golgi-resident TgDHHC5.