This thesis undertakes three separate lifecycle analyses to determine the emissions and fossil energy demand required to process algae biomass into renewable fuel and animal feed. A complete well-to-wheel fuel-cycle analysis is conducted for the production of biodiesel and jet biofuel from algae biomass. The environmental impacts of algae-based fuels for the road transportation and aviation industry are benchmarked against analogue conventional fossil fuels. This thesis demonstrates that algae biofuel production can only realize its inherent environmental advantage of reduced GHG emissions, once every step of the production chain is fully optimized and decarbonized. This includes smart co-product utilization, offsetting fertilizers through wastewater recycling, reusing exhaust gases as additional CO2 source and using decarbonized electricity, heat and indirect energy. The definition of a Catalyst Sensitivity Index (CSI) demonstrates how catalytic efficiency increases can impact the fossil energy consumption and the greenhouse gas emissions balance of catalyst-dependent processes. The CSI will allow the industry to highlight 'best practice catalysts' and draw conclusions for what efficiency gains one could anticipate with higher performance catalysts. For countries where a decarbonized electricity and heat grid is not available to guarantee low-carbon algae fuel production and the looming resource scarcity around marine feed production has become more pressing, the alternative use of algae for aquafeed production is recommended. This thesis analyses major routes towards the future cost-competitive production of microbial biomass as sustainable fish meal and oil source to meet a global demand for depleting fish feed supplies. A comprehensive economic cost analysis and lifecycle assessment demonstrates the feasibility of replacing global fish meal and fish oil supplies with low-carbon and affordable algae feed by the year 2030. This research reveals how algae feed production has the potential to transform a pressing resource tipping point into a turning point.