Empirical and theoretical consensus on how individual differences influence negotiation outcomes remains limited. Our preregistered research examines how 29 individual difference measures—identified through expert interviews and literature review—predict performance across five well-established negotiation tasks in a sample of N=238 experienced managers from 54 countries. This work advances past research by (a) predicting both distributive and integrative outcomes, (b) comparing data-driven findings with expert estimates (N=37), and (c) synthesizing predictors into a novel higher-order personality model for negotiation performance. Results show that agentic traits (e.g., extraversion, individualistic SVO) were linked to higher individual gains, while more communal traits (e.g., emotional intelligence, agreeableness) coincided with lower individual performance. Joint gains increased with honesty and self-efficacy. Personality scholars surprisingly overestimated the predictive power of individual traits and overlooked detrimental effects. We propose a latent variable-based framework of four factors that jointly and interactively predict negotiation success and discuss implications for negotiation research and practice.