Biological nitrogen fixation is an essential metabolism for sustaining global ocean productivity. Investigations over the past century have particularly established the biogeochemical and ecological significance of diazotrophs in surface waters and select coastal environments, and recent work has noted that some marine sediments representative of the broader seafloor also host active diazotrophs. Here, we use nifH amplicon sequencing to investigate the phylogenetic diversity and changes in community composition of potential diazotrophs in sediments along a 300 km continental margin transect. Although previous stable isotope tracer experiments did not detect active nitrogen fixation in these sediments, our molecular analyses suggest these sediments host phylogenetically diverse diazotrophs. We propose that marine sediments may serve as sources of fixed nitrogen when suitable environmental conditions arise.