Marine-derived fungi are considered to be valuable producers of bioactive secondary metabolites used as lead compounds with medicinal importance. In this study, chemical investigation of the seawater-derived fungus SW9 led to the isolation and identification of one new quinazolinone alkaloid, 2-(4-hydroxybenzyl)-4-(3-acetyl)quinazolin-one (), one new aromatic bisabolene-type sesquiterpenoid, () and one new chorismic acid analogue (), as well as two known alkaloids (compounds and ). Their structures were determined by extensive 1D/2D NMR and mass spectrometric data, and the absolute configurations of and were assigned by the analysis of ECD spectra aided by quantum chemical computations. Compounds , and exhibited selective inhibitory activities against the human pathogenic bacteria , , and , with MIC values ranging from 2.0 to 16 μg/mL.