The individual parties in Congress make standing committee assignments before the parties put the final assignments up to a vote on the floor of the U.S. House or U.S. Senate. The composition of each committee is a ratio of each chamber for the majority and the minority parties. Members go through a party process to determine assignment of each committee.
In the first step of the assignment process, members declare committee preferences to the party’s selection committee. The committee considers internal politics, such as seniority, to determine the assignments. After a certain allocation of committee seats, the U.S. Senate uses randomization to determine the assignments of new members. Seniority plays a larger role in the assignment of leadership positions within committees, such as Chairperson. Each chamber uses specific party rules to guide this process, but the Senate chamber uses a more formal process to which both parties typically adhere.
Finally, the party leaders combine assignments, and the measure meets for approval on the floor of each respective chamber. This generally occurs without deadlock as the work for committee assignment occurs before the legislative session officially begins.
Select committees and joint committees have much of the same approval process. Senior party officials, however, have even greater influence for appointment to these committees.