Under Section 7, paragraph 5 of the Act of the United States Congress of 01 July 1902, the authority to judge the election, returns and qualifications of members of the Legislature was an exclusive prerogative vested with the National Assembly. The subsequent shift to bicameral legislature did not change, but in fact further emphasized such exclusivity. The Act of the United States Congress of 29 August 1916, which created a bicameral legislature, provided that “the Senate and House of Representatives, respectively, shall be the sole judges of the elections, returns, and qualifications of their elective members x x x.” (Section 18, paragraph 1.).  Thus, neither house could interfere with the judgment of the other, nor could the courts take cognizance of the subject matter.

With the return to a unicameral legislature under the 1935 Constitution, the power traditionally vested in the legislative body was transferred to an independent, impartial, non-partisan tribunal called the Electoral Commission.  Article VI, Section 4 of the 1935 Constitution created an “Electoral Commission composed of three justices of the Supreme Court designated by the Chief Justice and six members chosen by the National Assembly, three of whom shall be nominated by the party having the largest number of votes therein. x x x. The Electoral Commission shall be the sole judge of all contests relating to the election, returns, and qualifications of all members of the National Assembly.”

On 11 April 1940, the second National Assembly amended the 1935 Constitution.  By virtue of Resolution No. 73, a bicameral legislature was established and an electoral tribunal for the Senate of the Philippines was created.  As amended, Article VI, Section 11 of the 1935 Constitution read: “The Senate xxx shall xxx have an Electoral Tribunal which be the sole judge of all contests relating to the election, returns and qualifications of (its) members.”

Parenthetically, 11 April 1940, the date of approval of Resolution No. 73 by the National Assembly creating the Senate Electoral Tribunal is considered the Foundation Day of the Tribunal.  The declaration was made in Resolution No. 10, Series of 2002 dated 08 August 2002, to accord due recognition to this significant event in the history of the Tribunal and to establish a tradition of commemorating its creation.

Notwithstanding, it was only in 1946 that the Senate Electoral Tribunal was finally constituted.  War broke out and the elections under the 1940 constitutional amendment could be held only on 23 April 1946.  The Senators elected therein assumed office on 25 May 1946, on which date, then Supreme Court Chief Justice Manuel V. Moran transmitted to the Senate of the Philippines the designation of Justices Ricardo M. ParasEmilio Y. Hilado and Gregorio M. Perfecto as members of the Senate Electoral Tribunal.  The composition of the Tribunal was completed two (2) days later, on 27 May 1946, with the nomination of the following Senators: Vicente J. FranciscoDomingo F. Imperial and Proceso E. Sebastian (for the Majority); and Nicolas B. BuendiaPedro C. Hernaez and Eulogio A. Rodriguez, Sr. (for the Minority).

Eleven (11) days later, or on 07 June 1946, the Tribunal approved the Rules of the Tribunal and less than a year later, on 19 April 1947, it promulgated its first decision.  In Case No. 1, entitled “Prospero Sanidad, Vicente dela Cruz and Servillano de la Cruz, Protestants vs. Ramon Diokno, Jose O. Vera, and Jose A. Romero, Protestees, the Tribunal declared Protestant Sanidad and Protestees Vera and Diokno as duly elected senators. By that time, the senatorial component of the Tribunal had changed thus:

The Senate Electoral Tribunal did not exist in the parliamentary form of government under the 1973 Constitution. Jurisdiction over electoral protests involving the Members of the Batas Pambansa was vested in the Commission on Elections (COMELEC).  The jurisdiction was returned to the present Senate Electoral Tribunal under the 1987 Constitution.

On 26 August 1987,  the reconstituted Tribunal held its organizational meeting under Senior Associate Justice Pedro L. Yap as Chairperson with Associate Justices  Andres R. Narvasa and Hugo E. Gutierrez, Jr. and Senators Neptali A. GonzalesJoseph E. EstradaTeofisto B. Guingona, Jr.Jose D. Lina, Jr., Mamintal A. J. Tamano and Victor S. Ziga, as members.

Since then, the following Justices served as Tribunal Chairperson: Andres R. NarvasaHugo E. Gutierrez, Jr.Isagani A. CruzTeodoro R. PadillaFlorentino P. FelicianoFlorenz D. RegaladoFlerida Ruth Pineda-RomeroJosue N. Bellosillo, Reynato S. Puno, Leonardo A. Quisumbing, Antonio T. Carpio, and Estela M. Perlas – Bernabe.

On 14 May 2022, Senior Associate Justice Marvic Mario Victor F. Leonen was designated by the Chief Justice as Chairperson of the Tribunal and remains as such to this day.