A robust relationship between working memory (WM) and general intelligence (g) has been well established. Nevertheless, explanations for this relationship in terms of underlying neurocognitive processes are still inadequate. This study addresses this issue using an individual differences approach in which Central Executive System (CES) and Short-Term Storage (STS) c o m p o n e n t s of WM are measured comprehensively and examined for their relationship with g via event-related potentials components (P200 and P300) as mediators. Participants (n=115) completed tests of the WM, CES and STS, as well as g. P200 and P300 components were recorded d u r i n g 3-back WM task performance. Structural equation modelling showed significant negative associations between the P200 latency for target stimuli a n d CES shifting processes, and between the P300 amplitude for target stimuli and CES inhibition and updating processes. The relationship between CES processes and g was mediated in a localized fashion by the P300 amplitude. These findings further support the notion that the CES has a multidimensional structure and, importantly, reveal that the inhibition and updating functions of the CES are crucial in explaining the relationship between WM and g. Negative relations between ERP indices (P200 latency and P300 amplitude for target stimuli) and g support a neural efficiency hypothesis related to high intelligence.