Whether a president should also serve as a party chairman has been a controversial issue in Taiwan. However, both the Kuomintang and the Democratic Progressive Party nodded in agreement on this issue as long as they were the ruling parties. Does the fusion of the two roles really make the passage of government bills easier? Most of the existing literature neglected the important factor of a president acting as a party chairman, and hence provided no answer to this question. In actual practice, we observed several cases of failures in securing the passage of government bills in the Legislative Yuan even after a president was named the chairman of the ruling party. In this article, we argue that, other factors being equal, the fusion of the two roles does enhance the probability of the passage of government bills. In our arguments, two reasons explain why this relation holds. Firstly, when a president acts as the party chairman, he/she does not need to rely on an agent to help him/her achieving policy goals, and can ensure the party’s policy preferences are exactly the same as his/her own. A president acting as a party chairman can also directly lead the party in the Legislative Yuan and better ensure support from the party’s legislators. Secondly, a president acting as party chairman also helps induce a more cooperative stance among the opposition parties because of the following reasons. The first is that a more cohesive ruling party under a president’s leadership as the party chairman is more likely to gain public support, which in turn makes opposition parties more likely to adopt more cooperative stances on some government bills. The second is that a president acting as a party chairman will help his party policy stances move closer to those of the median voter, and these policy stances will be more likely to gain public support, inducing opposition parties to follow suit, at least on some government bills. The empirical findings provide supportive evidence for the hypothesis of this article.