Acinetobacter baumannii is an important opportunistic pathogen known for its high levels of resistance to many antibiotics, particularly those considered last resort such as colistin and carbapenems. Plasmids of this organism are increasingly associated with the spread of clinically important antibiotic-resistance genes. Although A. baumannii is a ubiquitous organism, to date, most of the focus has been on studying strains recovered from clinical samples ignoring those isolated in the environment (e.g., soil, water, food etc.). Here, we analysed the genetic structures of plasmids found in s set of 18 environmental Acinetobacter strains. Genomes were sequenced using a combination of short-read Illumina and long-read MinION (Oxford Nanopore) sequence data using a hybrid assembly approach. Several novel plasmids were found including a large plasmid (p8E072658) that carries a new variant of the mcr-4 colistin resistance gene (mcr-4.7) in a novel Tn3 transposon (called Tn6926) carried. Analysis of novel plasmids showed several modules shared by plasmids frequently found in globally distributed clinical strains. Detailed analysis of the genetic structure of novel plasmids carried by environmental strains also showed a complex evolutionary history revealing genetic exchange events within the Acinetobacter genus beyond the strains’ clinical or environmental origin. This work provides evidence that environmental strains might act as a source for some of the clinically significant antibiotic-resistance genes. This study also calls for further investigation of environmental strains to reveal the intricacies of the origin and evolution of antibiotic resistance.