Empirical studies show a link between substantive and descriptive representation of racial and ethnic minorities. However, our understanding of the mechanisms through which this association operates comes almost exclusively from normative arguments. This article examines three of these proposed mechanisms: two intrinsic mechanisms operationalised as perceptions of shared experience and a motivation to represent, and an extrinsic mechanism of electoral incentives. By doing so it moves on from documenting the link between descriptive and substantive representation to explaining it. Clear evidence is found that prospective minority representatives are influenced by all three motivations, to different extents, with a difference between minority candidates of different parties. Also, while the ethnic minority population of a constituency is usually associated with extrinsic motivation, it is found that it increases intrinsic motivation for representation among prospective minority representatives, suggesting these may be less distinct than is assumed in the normative literature.