Ganoderma multipileum Ding Hou is a laccate polypore investigated here through an integrated taxonomic, phytochemical, antioxidant, nanoparticle-synthesis, and antibacterial study. Basidiomata were collected during a macrofungal survey at Government College for Women, Vazhuthacaud, Thiruvananthapuram, Keralamm, India, in June 2025. Identification was based on macroscopic and microscopic characters and nrITS sequence analysis. The sequence generated in the study was deposited in GenBank under accession PZ587000 and clustered with reference sequences of G. multipileum in a maximum-likelihood phylogeny, with 62% bootstrap support. Methanolic and aqueous extracts yielded 8.2% and 11.2%, respectively. Qualitative screening recorded several metabolite classes in the extracts. Total phenolic content was reported as 53 mg GAE/g extract for the methanolic extract and 51 mg GAE/g for the aqueous extract; total flavonoid content was 26 mg QE/g and 22 mg QE/g, respectively. Total terpenoid content was reported as 3.6% (w/w). The methanolic extract showed concentration-dependent activity in DPPH, ABTS, and FRAP assays. Green synthesis using the aqueous mushroom extract produced silver and copper nanoparticle preparations with UV–Visible absorbance maxima at 400–410 nm and approximately 560 nm, respectively. In agar disc diffusion tests against Escherichia coli and Bacillus cereus, the crude methanolic extract produced inhibition zones up to 15 mm; silver nanoparticle preparations produced zones up to 18 mm against B. cereus, while copper nanoparticle preparations produced a 20 mm zone against E. coli. The study documents the taxonomic identity and in vitro phytochemical, antioxidant, and antibacterial observations reported for G. multipileum collected in Keralamm.