Soils, if designed and managed correctly, can retain carbon from the atmosphere as accumulated organic matter, refractory forms of carbon (e.g. biochar) or stable, inorganic, carbonate minerals. This soil ‘carbon capture function’ is highly applicable to the constructed environment in urban areas and should be considered when planning for new or existing developments. The total carbon capture potential of soils in cities may be as high as 7 Mt/year within the UK using biochar and accumulated carbonate minerals, which is equivalent in significance to other forms of geoengineering. Furthermore, soil and vegetation management practices may be implemented to accumulate plant-derived organic carbon in urban soils. The potential for substantial soil-based carbon sequestration in urban environments has yet to be realised, and the varied praxis of soil carbon capture presents accreditation and regulatory challenges to the planning system which need to be resolved.