This branch is overseen by the SA Executive Board (E-Board), which consists of the president, vice president, treasurer, who are elected each spring semester. Their responsibilities include overseeing and enforcing the SA by-laws and serving as the leading advocates for the undergraduate student body.

This branch contains the SA Senate, which is responsible for the allocation of the SA budget and the recognition/derecognition of SA clubs. The Senate determines the annual budgetary allocations for clubs based on recommendations by the Board of Directors Finance Committee. The Senate Board of Directors is comprised of 23 members. 11 directors are members by virtue of their offices within SA (3 E-Board members, 7 council coordinators elected by their respective councils, and the Student Affairs director). The remaining 12 directors are elected by the undergraduate students at the beginning of the fall semester. The Senate also enacts resolutions concerning issues of importance to the undergraduate student body in regards to issues of academic policy, student rights, and student welfare. The Senate may also create ad hoc positions, agencies, task forces, and committees to take action on any of the aforementioned items.

UB's Student-Wide Judiciary is a legally separate student group unrelated to SA that has the authority to hear non-financial disputes between SA and its members but is subject to any limitations contained in SA's By-Laws and policies. Only Student-Wide Judiciary justices who are also members of SA may participate in the adjudication of any dispute concerning SA. The Student-Wide Judiciary may not compel SA to violate any University at Buffalo rule or policy, nor any binding law or regulation. Any determination by the Student-Wide Judiciary that contradicts a University at Buffalo rile or policy or any binding law or regulation shall be considered void ab initio. SA officers, directors, assembly members, and employees may rely in good faith on the written advice of a University at Buffalo official as to whether a particular Student-Wide Judiciary ruling contradicts any University at Buffalo rule or policy or any binding law or regulation.