The rising number of women in Congress changes deliberation. Using committee hearing transcripts from 1995 to 2017, we analyze how the gender composition of committees affects group dynamics in committee hearings. While we find limited evidence that increasing proportions of women affects women’s participation, we find that discussion norms within committees change significantly in the presence of more women. Namely, interruptions decrease when there are more women on the committee; with higher proportions of women, men are less likely to interrupt others. Furthermore, committee members are more likely to engage and stay on the same topics in the presence of more women, suggesting a shift in norms toward more in-depth exchange. Overall, our results show that increasing the proportion of women changes discussion dynamics within Congress by shifting norms away from interruptions and one-sided talk in committees, thereby shifting group norms that govern decision-making during an important policy-making stage.