The microbial community mediated biogeochemical cycles play important role in global C-cycle and display a sensitive response to environmental changes. Limited information is available on microbial composition and functional diversity controlling biogeochemical cycles in the riverine environment. The Ganga River water and sediment samples were studied for environmental gene tags with reference to carbohydrate metabolism, photoheterotrophy and chemolithotrophy using high throughput shotgun metagenomic sequencing and functional annotation. The diversity of environmental gene tags specific microbial community was annotated against reference sequence database using Kaiju taxonomic classifier. The metagenomic analyses revealed that the river harbored a broad range of carbohydrate and energy metabolism genes. The in-depth investigation of metagenomic data revealed that the enzymes associated with reverse TCA cycle, Calvin-Benson cycle enzyme RuBisCO, starch and sucrose metabolism genes were highly abundant. The enzymes associated with sulfur metabolism such as EC:2.7.7.4 (sulfate to ammonium per sulfate), EC:1.8.1.2, EC:1.8.7.1 (sulfite to H2S) were prevalent in both the class of samples. The principal component analysis of the functional profiles revealed that the water and sediment samples were clustered distinctly suggesting that both the sites had variable abundance of functional genes and associated microbiota. The taxonomic classification showed abundance of Proteobacteria, Actinobacteria and Bacteroidetes phyla. Also, the metagenomic study showed the presence of purple sulfur bacteria viz. Thiodictyon, Nitrosococcus and purple non-sulfur bacteria viz. Bradyrhozobium and Rhodobacter. The study demonstrates that the Ganga River microbiome has prevalence of functional genes involved in carbohydrate anabolism and catabolism, and CO2 fixation with great prospects in cellulose and sulfide degrading enzyme production and characterization. •River Ganga harbored broad range of carbohydrate and energy metabolism genes.•Enzymes involved in reverse TCA, Calvin-Benson cycle enzyme RuBisCO were prevalent.•Sulfur metabolism enzymes such as EC:2.7.7.4 and EC:1.8.1.2 were prevalent river.•Proteobacteria, Actinobacteria and Bacteroidetes were the highly abundant phyla.•Various purple sulfur and purple non sulfur bacteria were also detected.