The compliance of the chemical and environmental requirements for using woody biomass fly ash (WBFA) as a mineral admixture in cement-based materials was studied in terms of the use of the cement-biomass fly ash concrete where the fluids surrounding and interacting with it renew themselves over time. The study was preceded by a preliminary characterization of WBFA whose results showed that the European chemical requirements (EN 450-1, 2012) established for the reuse of coal fly ash in cement-based materials (there is no normative for WBFA) were met except for the chloride content. A blend with a quite high content of WBFA (30%) and Portland cement (70%) was prepared to test the leaching behaviour of the cement-biomass fly ash concrete. After that, cubic specimens were cast from a paste with water:solid ratio 0.5 and subsequently cured for 28 days at 20 °C. Monolith leaching tests were carried out on the specimens for heavy metals leachability, following the standard leaching test NEN 7345 that was modified to make it able to simulate an aggressive environmental context where the hardened cementitious material was supposed to be placed. The results have shown a good capacity of the cement-biomass fly ash material to immobilize the heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) present in the WBFA. Also, the extrapolated releases of these metals after 100 years were found below the limits established by the Dutch Building Materials Decree. Thus, the reuse of WBFA in cement-based materials may be considered compatible with the environmental requirements.