In 2018, secular, or nonreligious individuals, became the largest "religious" group in America surpassing Evangelical Christians. Their rise has been meteoric. Beginning in the early 1990s, seculars now make up nearly 25 percent of the population. This trend is also political as seculars tend to identify with the Democratic Party and take liberal positions on cultural issues such as same-sex marriage and abortion. Seculars in American politics may be especially impactful as previous research has shown that politics, and the connection between religion and politics, drives individuals away from religion. But despite attention to the political causes of rising secularism in the United States, much less is known about the political consequences. If a rejection of the religious right in the Republican Party drives individuals away from religion, then secularism may also push individuals toward the Democratic Party. The tendency of seculars to be Democratic coupled with their rise as a proportion of the population may point to a long-term electoral advantage for the Democratic Party. Currently, however, the Democratic Party has been hesitant to run secular candidates for public office and speak openly about secularism and nonreligion. Despite the strong presence of seculars in the Democratic Party, most Democrats are religious and many, including Black Protestants and Hispanic Catholics, are highly religious. How then might seculars have political influence? And can the Democratic Party benefit from the involvement of seculars in the Party? Despite their reputation as "nones" or disaffected atheists, "active" and "committed" seculars strongly identify with the Democratic Party and have the potential to exercise influence through participation and activism. Political activism, especially through political parties, is an important mechanism for the political incorporation of new groups. Activists are also critical for political parties as activists contribute money, work on campaigns, and volunteer for the party organization. It is the purpose of this dissertation to investigate the process of secular incorporation into the party system by focusing on secular activism. I will show that secular grassroots activists are already prominent in the Democratic Party, but also that secular activists are less involved in party politics than their nonsecular counterparts. Secular activists are also ideologically extreme, which suggests secular activists may push the Democratic to take more liberal policy positions. I also use experimental evidence to show that secular activists desire representation, and that appeals to secular activists would lead seculars to be more likely to vote for a secular candidate. These findings suggest that secular may form a new, important group in the Democratic Party and may reshape the candidates and policy positions the Party supports.