This article presents large‐sample developmental and validation research for a set of research scales of an existing 360‐degree personality measure, the LMAP 360 (Leadership Multi‐rater Assessment of Personality). In Study 1 (N = 1,771), we identified 6 broad domains underlying LMAP item clusters: Neuroticism, Dominance, Enthusiasm, Openness, Agreeableness, and Conscientiousness. Scales measuring these broad domains and their constituent facets showed strong internal consistency, inter‐rater reliability, and self‐informant correlations. In Study 2 (N = 729 and N = 694), we examined LMAP research scales’ convergent and discriminant validity against three well‐validated personality inventories (Goldberg's adjectives, the Big Five Inventory, and the Big Five Aspects Scales) and one measure of cognitive ability (the International Cognitive Ability Resource). LMAP research scales correlated strongly with corresponding scales from other inventories and were distinct from cognitive ability.