Empirical evidence on the external knowledge search behaviour of construction firms and its effects on innovation ambidexterity (IA) and performance is limited. The purpose of this study is to examine the effects of external knowledge sources on IA and the mediating role of IA in the relationship between external knowledge sources and financial performance (FP) in construction firms. It tests the hypotheses developed using survey responses from management personnel in Hong Kong construction firms. The results indicate that knowledge from clients or suppliers has a significant effect on IA. Similarly, knowledge sourced from universities and research institutions has a significant positive impact on IA. However, only knowledge from clients directly affects FP. IA fully mediates the relationships between knowledge from clients, suppliers or universities and research institutions with FP but not the other three sources. While partly validating some existing studies, these findings also extend the current knowledge on the connection between external knowledge sources and IA. This shows how IA can translate external knowledge into financial outcomes, revealing the value of different knowledge sources for firms. The findings provide insights into how construction firms can direct their knowledge searches to enhance ambidexterity and financial outcomes. This study showed the importance of external collaborators for construction firms in achieving IA and FP. It contributes to the theory and practice on the antecedents and outcomes of IA in construction firms and the path-dependent processes to enhance FP through the use of external knowledge to simultaneously pursue exploratory and exploitative innovation. © 2023 Informa UK Limited, trading as Taylor & Francis Group.