The fungal strain BC17 was isolated from sediments collected in the intertidal zone of the inner Bay of Cadiz and characterized as Emericellopsis maritima. On the basis of the one strain–many compounds (OSMAC) approach, four new eremophilane-type sesquiterpenes (1–4), together with thirteen known derivatives (5–17) and two reported diketopiperazines (18, 19), were isolated from this strain. The chemical structures and absolute configurations of the new compounds were determined through extensive NMR and HRESIMS spectroscopic studies and ECD calculation. Thirteen of the isolated eremophilanes were examined for cytotoxic and antimicrobial activities. PR toxin (16) exhibited cytotoxic activity against HepG2, MCF-7, A549, A2058, and Mia PaCa-2 human cancer cell lines with IC50 values ranging from 3.75 to 33.44 µM. (+)-Aristolochene (10) exhibited selective activity against the fungal strains Aspergillus fumigatus ATCC46645 and Candida albicans ATCC64124 at 471 µM.