Over half of the global raw materials are consumed in the construction of buildings and roads, their associated greenhouse gas emissions from excavation to final disposal are pivotal to the change in global climate. Hemp is a natural resource that has recently been used as a low environmental impact material in a number of composite products. In buildings, it is increasingly used with a lime base binder in wall constructions. There are limited data available to evaluate the environmental impact of this type of construction in the UK. This research aims to identify the processes and materials involved in the construction of hemp–lime walls and to establish their life cycle impact on climate change. The study follows assessment procedures and guidelines of international (ISO14040) and UK (PAS2050) standards. The functional unit defined for the hemp–lime wall construction is 1 m square in area, 300 mm thick with timber frame support inside. Primary data were collected for processes and materials that have no existing information. Other processes with impact data available from credible database were adapted in the assessment by taking into account the conditions and practice in the UK. Assessment was carried out using the SimaPro LCA tool over a lifetime of 100 years. Within the boundary and assumptions made, results showed the functional unit could sequestrate 82.7 kg of carbon dioxide with a net life cycle reduction of greenhouse gas emission of 36.08 kg CO2e.