The construction industry is responsible for 20% of the global greenhouse gas emissions (GHG), of which around 12% are attributable to concrete. Around 6 billion m2 of floor space is expected to increase yearly to accommodate the growing global urban population. The demographics of urban growth are concentrated in the global south, where the utilisation of low-strength concrete blocks as a wall element is predominant. Moreover, the literature indicates that high cement content is normally used in block manufacturing. Hence, there is a clear need to develop a low-cost environmental solution for concrete blocks. Therefore, this study aims to reduce the clinker content in the binder by 65% by using limestone calcined clay cement (i.e., LC3–35) and reduce the binder content in LC3 concrete hollow blocks to minimise CO2 emissions. As a result of the mix design optimisation and gradation of aggregates, the binder content in the blocks was reduced up to 100 kg/m3. A life cycle assessment highlighted the potential of synergic reduction in GHG in the developed LC3 concrete hollow block mixes without significantly affecting mechanical properties.