We examine the effects of national voter registration policies on voting patterns with a large-scale experimental study. Together with Kenya's electoral commission, we designed an experiment in which 1,674 communities were randomized to a status quo or treatment group, receiving civic education on voter registration, SMS reminders about registration opportunities, and/or local registration visits by election commission staff. We find little evidence that civic education improves registration. Local registration visits improve voter registration, a relationship that increases in poorer communities. Moreover, local registration increased electoral competition and vote preference diversity in down-ballot contests in the 2017 Kenyan elections. Our results suggest that status quo voter registration policies constrain political participation and competition, and that inexpensive policy changes may attenuate the effects of such constraints.