Cyanobacteria are complex prokaryotes, incorporating a Gram-negative cell wall and internal thylakoid membranes (TM). However, localisation of proteins within cyanobacterial cells is poorly understood. Using subcellular fractionation and quantitative proteomics we report the first subcellular map of the proteome of an entire cyanobacterial (or any other prokaryotic) cell, identifying ~67% of Synechocystis sp. PCC 6803 proteins, ~1000 more than previous studies. 1,712 proteins were assigned to six specific subcellular regions. Proteins involved in energy generation localised to TMs. The majority of transporters, with the exception of the TM localised copper importer CtaA, resided in the plasma membrane (PM). Most metabolic enzymes are soluble although numerous pathways terminated in the TM (notably those involved in peptidoglycan monomer, NADP+, heme, lipid and carotenoid biosynthesis), or the PM (specifically those catalysing lipopolysaccharide, molybdopterin, flavin adenine dinucleotide and menaquinone biosynthesis). Furthermore, we identified the proteins involved in the TM and PM electron transport chains. The majority of ribosomal proteins and enzymes synthesising the storage compound polyhydroxybuyrate formed distinct clusters within the data suggesting that they have similar subcellular distributions to one another as one would expect for proteins operating within multi-component protein structures. Moreover, heterogeneity within membrane and cytoplasmic regions is observed, indicating further cellular complexity. Cyanobacterial TM protein localisation is conserved in Arabidopsis thaliana chloroplasts, suggesting similar proteome organisation in higher photosynthetic organisms. The organisation of a cyanobacterial cell revealed here will significantly aid our understanding of these environmentally and biotechnological important organisms. The successful application of this technique in Synechocystis suggests it could be applied to mapping the proteomes of other cyanobacteria and complex single-celled organisms.