There has been surprisingly little consideration of how the selection of political candidates compares with employee selection, or whether individual differences predict electoral success. This study describes the design and validation of an assessment centre [AC] for selecting prospective Parliamentary candidates for a main UK political party. A job analysis was conducted to identify the key competencies required by a Member of Parliament [MP] and the selection criteria for a standardised assessment process. Analysis of the first 415 participants revealed no differences on exercises or dimensions in performance between male and female candidates. For the 106 candidates selected to fight the May 2005 UK general election, critical thinking skills [CTA] and performance in a structured interview were significantly associated with the ‘percentage swing’ achieved by a candidate (r = .45, p <.01; r = .31, p <.01). CTA was also associated with ‘percentage votes’ (r = .26, p <.01). These results are discussed in relation to the development of a theory of political performance