Strain HIMB55 is a phylogenetically unique member of the OM60/NOR5 clade of the Gammaproteobacteria isolated from coastal seawater of Kaneohe Bay on the northeastern shore of Oahu, Hawaii, by extinction culturing in seawater-based oligotrophic medium. Here we present the genome sequence of strain HIMB55, including genes for bacteriochlorophyll-based phototrophy.