Several years of research have been dedicated to investigating the question of why intelligent and experienced leaders are not always successful in spite of having high levels of cognitive intelligence (IQ) and the suitable personality traits. Emotional Intelligence (EI) gained considerable popularity from the notion that it may underlie various aspects of workplace performance that could not be accounted for by IQ or personality and that it could be developed in promising individuals. Adjunct to this, the field of Positive Organisational Scholarship underscored the importance of cultivating positive emotions in individual organizational members and others, not just as end-states in themselves, but also as a means to achieving individual and organizational transformation; and hence optimal functioning over time. The Swinburne University Emotional Intelligence Test (SUEIT) is one of numerous models and measures of EI that have consequently been developed. The development of this measure was aimed at providing an assessment of the most definitive dimensions of the construct by incorporating six of the predominant models and measures into the development of EI to provide an assessment of the most definitive dimensions of the construct.The current study was aimed at addressing the need for evidence in support of a self-report EI measures' utility to predict e.g. effective organizational leadership over and above other established constructs. Specifically the study aimed to provide support for the utility of the SUEIT to predict variance in leadership competence indicated by Assessment Centre (AC) technology results, not accounted for by other psychometric tools, namely the Occupational Personality Questionnaire (OPQ32i), measuring personality. One of the biggest issues currently facing measures of EI is the discriminant validity from measures of personality. Research was necessary to add to the body of knowledge with regards to the relationship between EI and effective leadership, and to provide support for the incremental validity of an EI measure to predict effective leadership over and above other wellestablished models and measures.The theoretical arguments that underlie the rationale for this study are encapsulated in the conceptual claims made about EI and organizational leadership, the IQ-EI debate as it pertains to leadership and the relationship between EI and effective leadership (i.e. the discriminant, predictive and incremental validity of EI related to organizational leadership). The constructs of EI, personality and AC leadership competencies were operationalised through the SUEIT, OPQ32i and leadership AC technology, iii respectively. The sample consisted of 49 < N < 112 (variation in the sample size was due to varying amount of missing cases in the different analyses done) middle managers from a company in the life assurance industry in South Africa. OPQ32i and AC data was extracted from archival records and EI data was collected on a separate occasion by means of an online version of the SUE...