Marine mammals have been described as sentinels of the health of marine ecosystems. Therefore, the aim of this study was to investigate (i) the presence of extended-spectrum β-lactamase (ESBL)- and AmpC-producing Enterobacterales, which comprise several bacterial families important to the healthcare sector, as well as (ii) the presence of Salmonella in these coastal animals. The antimicrobial resistance pheno- and genotypes, as well as biocide susceptibility of Enterobacterales isolated from stranded marine mammals, were determined prior to their rehabilitation. All E. coli isolates ( n = 27) were screened for virulence genes via DNA-based microarray, and twelve selected E. coli isolates were analyzed by whole-genome sequencing. Seventy-one percent of the Enterobacterales isolates exhibited a multidrug-resistant (MDR) pheno- and genotype. The gene bla CMY ( n = 51) was the predominant β-lactamase gene. In addition, bla TEM-1 ( n = 38), bla SHV-33 ( n = 8), bla CTX-M-15 ( n = 7), bla OXA-1 ( n = 7), bla SHV-11 ( n = 3), and bla DHA-1 ( n = 2) were detected. The most prevalent non-β-lactamase genes were sul2 ( n = 38), strA ( n = 34), strB ( n = 34), and tet(A) ( n = 34). Escherichia coli isolates belonging to the pandemic sequence types (STs) ST38, ST167, and ST648 were identified. Among Salmonella isolates ( n = 18), S. Havana was the most prevalent serotype. The present study revealed a high prevalence of MDR bacteria and the presence of pandemic high-risk clones, both of which are indicators of anthropogenic antimicrobial pollution, in marine mammals.