Campylobacter concisusis an emerging enteric pathogen that is associated with several gastrointestinal diseases, such as inflammatory bowel disease (IBD), which includes Crohn’s disease (CD) and ulcerative colitis (UC). Currently, only three completeC. concisusgenomes are available and more completeC. concisusgenomes are needed in order to better understand the genomic features and pathogenicity of this emerging pathogen. DNA extracted from 22C.concisusstrains were subjected to Oxford Nanopore genome sequencing. Complete genome assembly was performed using Nanopore genome data in combination with previously reported short-read Illumina data. Genome features of completeC. concisusgenomes were analysed using bioinformatic tools. The enteric disease associations ofC. concisusplasmids were examined using 239C.concisusstrains and confirmed using PCRs. Proteomic analysis was used to examine T6SS secreted proteins. We successfully obtained 13 completeC. concisusgenomes in this study. Analysis of 16 completeC. concisusgenomes (3 from public databases) identified multiple novel plasmids. pSma1 plasmid was found to be associated with severe UC. Sec-SRP, Tat and T6SS were found to be the main secretion systems inC. concisusand proteomic data showed a functional T6SS despite the lack of ClpV. T4SS was found in 25% of completeC. concisusgenomes. This study also found that GS2 strains had larger genomes and higher GC content than GS1 strains and more often had plasmids. In conclusion, this study provides fundamental genomic data for understandingC. concisusplasmids, genomospecies features, evolution, secretion systems and pathogenicity.