A new examination of the linkages between electoral competition and the development of partisan organizations with their relationship to roll-call voting is generated. The study found a close association between variable electoral contestation, competition and success of minority parties in formerly one-party state house legislative chambers and the development of both minority and majority party organizations in these chambers. The model linked the features of increasing electoral competition to the development of greater chamber competition, greater proportional representation on substantive committees for the minority party, and the development of caucus organizations. These features of party organization, in turn, were linked to increasing intra-party cohesion and decreasing partisan conflict in roll-call voting in the chambers. The study is a comparative cross-state cross-time study of chambers which have formerly been one-party dominant.