The construction industry continues to play a significant role in the economic development of most nations in the world. However, the construction sector still follows the ‘linear’ ‘take–make–dispose’ industrial model that, having benefited development, plays a major factor in the depletion of resources, environmental deterioration, and the generation of waste and pollution. In this regard, the adoption of a circular economy (CE) presents a compelling opportunity to address the challenges derived from the traditional linear economic model. This study attempts to scrutinise the critical success factors (CSFs) for implementing a CE via a mixed-method approach that combines both focus groups and an online survey. The adopted approach ensures a comprehensive identification and prioritisation of CSFs for implementing CE principles in building construction projects. The focus groups consisted of 20 key stakeholders drawn from prominent construction firms which included clients, consultants, contractors and designers. The outcomes from these focused groups led to the dentification of 43 CSFs, later categorised across different dimensions. Subsequently, an online survey was conducted to establish a priority list of the identified CSFs, using responses from 82 stakeholders to rate their level of importance. The top five significant CSFs include ensuring the use of standardised and warranted secondary materials, maintaining cost equivalence between a CE and linear approach, maintenance and operation cost minimisation, assessment of life cycle cost (LCC), and the enforcement of robust government regulations and policies that prioritise a CE. The Relative Importance Index (RII) was used to rank the identified CSFs following results obtained using the Statistical Package for Social Sciences (SPSS 27) and Excel for Microsoft 365. The findings of this study can inform the creation of decision support systems that could progress a CE across the construction project life cycle.