The fungus Xylaria sp. Z184, harvested from the leaves of Fallopia convolvulus (L.) Á. Löve, has been isolated for the first time. Chemical investigation of the methanol extract of this strain’s culture broth led to the discovery of three new pyranone derivatives fallopiaxylaresters A-C (1–3) and a new bisabolane-type sesquiterpenoid named fallopiaxylarol A (4), along with the first complete set of spectroscopic data for the previously-reported pestalotiopyrone M (5). Known pyranone derivatives (6–11), sesquiterpenoids (12–14), isocoumarin derivatives (15–17), and an aromatic allenic ether (18) were co-isolated. Their structures were elucidated by the interpretation of HRESIMS, 1D, 2D NMR spectroscopy and quantum chemical computation method. The antimicrobial, anti-inflammatory, and α-glucosidase inhibitory activities of selected compounds and crude extract were evaluated in vitro. The extract inhibited nitric oxide (NO) production induced by lipopolysaccharide (LPS) in murine RAW264.7 macrophage cells, with an inhibition rate of 77.28 ± 0.82% at a concentration of 50 μg/mL. The compounds 5, 7 and 8 displayed weak antibacterial activity against Staphylococcus areus subsp. aureus at a concentration of 100 μM.