This empirical study of 323 new ventures examines how task and relationship conflict in the founding top management team mediates the effect of lead founder personality on new venture performance. The results reveal that (1) openness and agreeableness increase task conflict, whereas conscientiousness decreases it, and (2) openness, extraversion, and conscientiousness decrease relationship conflict, whereas neuroticism increases it. Furthermore, task conflict increases venture performance, whereas relationship conflict decreases venture performance and weakens the positive effect of task conflict. In addition, task and relationship conflict do not mediate the effect of extraversion, and they only partially mediate the effects of openness and neuroticism on new venture performance. Openness and neuroticism exert a direct impact on new venture performance, in addition to their indirect impact through task and relationship conflict.