The disclosed technology provides processes for producing hydrogen that is renewable, has negative carbon intensity, and is associated with net water production. The hydrogen is economically, environmentally, and socially superior to conventional hydrogen via steam reforming of natural gas or electrolysis of water. Some variations provide a process for manufacturing carbon-negative hydrogen and optionally activated carbon, comprising: feeding biomass into a first heated vessel or zone to generate dried biomass and a first recovered water stream; feeding the dried biomass into a second heated vessel or zone to pyrolyze the dried biomass, generating a biocatalyst and a biogas; feeding the biocatalyst, the first recovered water stream, and biogas to a third heated vessel or zone for biocatalytic conversion, thereby generating H2, CO, and optionally activated carbon; and recovering the hydrogen. The H2 is carbon-negative hydrogen characterized by a carbon intensity less than 0 kg CO2e per metric ton H2.