The effect of being the winner (vs. being the runner-up) on winning subsequent elections has been estimated across a series of countries using regression discontinuity design. We contribute to this literature by incorporating politicians who move across constituencies. The US and the UK are our case studies. UK–US differences are not apparent when comparing estimates of the individual incumbency advantage, i.e., winning the same office in the same constituency. UK–US differences in the career advantage of winning office are almost entirely driven by the ability of the UK's close-race runners-up to win elsewhere subsequently. Runners-up are more likely to move to safer seats. Marginal winners become locked-in to their seat. In the US, we observe negligible movement across constituencies. © 2023 The Authors