Biochar made from seaweed biomass of marine farms established for water pollutant remediation may be a promising amendment for soil remediation in the same coastal territory. The study aimed to assess the soil Cu-immobilizing, pH neutralizing, and nutrient improvement capabilities of a seaweed biochar when incorporated into degraded soil of the same coastal territory (Puchuncaví District, central Chile). Experimental design considered five treatments; degraded soil of Puchuncaví valley (C-), C- amended with either local seaweed biochar (B), vermicompost (V), or its mixture (BV), and a background soil (C+). Experimental soils were placed in pots and kept in a greenhouse (4 weeks). Lolium perenne was then sown and cultivated until week 11. Treatments amended with biochar (B and BV) significantly increased soil pH, available nitrogen and decreased Cu2+ ions. These treatments reached very high EC values but had no negative effect on plant yield. Regarding plant growth, V and BV significantly increased biomass, but V resulted in higher yield because of its higher nutritional status. It was concluded that seaweed biochar, made from local seaweed biomass of a coastal marine water pollutant remediation farm, may be an effective soil amendment for degraded soils of the same coastal territory, although its combination with an organic amendment should be considered.