Not all pieces of legislation introduced for consideration are equally likely to be successful. The characteristics of legislation’s cosponsors can influence bill passage rates. Despite facing marginalization in legislative bodies and more electoral vulnerability, women are effective lawmakers. We argue that one way by which women overcome marginalization and gendered expectations of performance is bill success from legislation cosponsored with other women. Testing this expectation on bills (140,000+) introduced in U.S. state legislatures in forty states in 2015, we find increased bill success from women’s cosponsorship with each other and women from the other party. Using variation in the share of women in legislative chambers and in legislative leadership, we find evidence to suggest that women’s success emerges both from marginalization and gendered opportunities.