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The occurrence of <i>Listeria monocytogenes</i> in marine fish and fish market areas was investigated. Two hundred and eighty-eight samples (123 environmental samples—siphons, knives, cutting boards, floor, sinks, water, and ice—and 165 marine fish samples) were examined. Twenty-four isolates were characterized as <i>Listeria monocytogenes</i> (five from environmental samples (4.0%) and 19 from fish samples (11.5%)). The strains were further characterized according to their antibiotic resistance, pathogenicity, and biofilm formation ability. They were molecularly serotyped as IIc (n = 22) and IVb (n = 2) and possessed all the virulence genes tested (<i>inlA</i>, <i>inlB</i>, <i>inlC</i>, <i>inlJ</i>, <i>actA</i>, <i>hlyA</i>, <i>iap</i>, <i>plcA</i>, and <i>prfA</i>), except for two strains lacking the <i>hlyA</i> and <i>iap</i> genes, respectively. All strains showed strong (41.7%) or moderate biofilm-producing ability (58.3%) and almost all showed resistance to at least one antibiotic, with the highest rates being observed against clindamycin and vancomycin. The proteomic analysis by MALDI-TOF revealed two distinct clusters that involved strains from fish only and those from both fish and the environment. The presence of <i>Listeria monocytogenes</i> in the fish-market environment and marine fish, along with the pathogenicity and persistence characteristics of the seafood-related strains, emphasize the need for vigilance concerning the spread of this notorious foodborne pathogen.