The president pro tempore is elected by the Senate as a whole, usually by a resolution which is adopted by unanimous consent without a formal vote.

[3] Since 1945, the most senior U.S. senator in the majority party has generally (though not always) been chosen to be president pro tempore and holds the office continuously until the election of another.

Although the position is in some ways analogous to the speaker of the United States House of Representatives, the powers of the president pro tempore are far more limited.

[7] Additional duties include appointment of various congressional officers, certain commissions, advisory boards, and committees.

[9] The first president pro tempore, John Langdon, was elected on April 6, 1789,[6] serving four separate terms between 1789 and 1793.

Still president pro tempore at that time, he would have temporally become the acting president had the Electoral College vote not been certified by March 4, 1877; Congress certified Rutherford B. Hayes as the winner of the Electoral College vote on March 2.

[17][18] The president pro tempore and the speaker of the House were removed from the presidential line of succession in 1886.

Electing his successor proved difficult, as Senate Republicans, then in the majority, were split between progressive and conservative factions, each promoting its own candidate.

It took four months for a compromise solution to emerge: Democrat Augustus Bacon served for a single day, August 14, 1911, during the vice president's absence.

Thereafter, Bacon and four Republicans—Charles Curtis, Jacob Gallinger, Henry Cabot Lodge, and Frank Brandegee—alternated as president pro tempore for the remainder of that Congress's session.

Patty Murray was elected president pro tempore in January 2023, the first woman to hold the position.

With the ratification of the Twenty-fifth Amendment to the United States Constitution in 1967, vacancies in the vice presidency became much less common.

It has been held by Strom Thurmond (R-South Carolina) (2001–2003), Robert Byrd (D-West Virginia) (2003–2007), Ted Stevens (R-Alaska) (2007–2009), Patrick Leahy (D-Vermont) (2015–2021), Chuck Grassley (R-Iowa) (2021–2025), and Patty Murray (D-Washington) (2025–present).

[25] With the change in party control, Democrat Robert Byrd of West Virginia replaced Thurmond as president pro tempore, reclaiming a position he had previously held from 1989 to 1995 and briefly in January 2001.

[8] Although a president pro tempore emeritus has no official duties, they are entitled to an increase in staff,[26] and advise party leaders on the functions of the Senate.