A novel marine Gram-stain-negative, aerobic, rod-shaped bacterium, designated as strain PS1^T, was isolated from the deep-sea sediments of the Mariana Trench and characterized phylogenetically and phenotypically. Bacterial optimal growth occurred at 35 °C (ranging 10–45 °C), pH 6 (ranging pH 5–10) and with 11% (w/v) NaCl (ranging 0–17%). The 16S rRNA gene sequence similarity results revealed that strain PS1^T was most closely related to Pseudomonas stutzeri ATCC 17588^T, Pseudomonas nitrititolerans GL14^T, Pseudomonas zhaodongensis NEAU-ST5-21^T, Pseudomonas xanthomarina DSM 18231^T and Pseudomonas kunmingensis HL22-2^T with 98.3–98.7%. The digital DNA–DNA hybridization values and the average nucleotide identity between strain PS1^T and the reference strains were 20.4–40.1% and 78.7–79.4%, respectively. The major respiratory quinone is ubiquinone Q-9. The major polar lipids were phosphatidylethanolamine, diphosphatidyglycerol, phosphatidylglycerol, phosphatidylcholine, aminoglycolipid, two unidentified glycolipids and one unidentified lipid. The predominant cellular fatty acids of strain PS1^T were summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), summed feature 3 (C_16:1ω7c and/or C_16:1ω6c), C_16:0 and cyclo-C_19:0 ω8c. The G + C content of the genomic DNA was 63.0%. The combined genotypic and phenotypic data indicated that strain PS1^T represents a novel species of the genus Pseudomonas, for which the name Pseudomonas marianensis sp. nov. is proposed, with the type strain PS1^T (= DSM 112238^T = MCCC 1K05112^T).