Updated at 5:06 p.m. ET
Democrats officially took control of the Senate as Georgia's two new Democratic senators-elect were sworn in Wednesday afternoon, cementing a 50-50 split, with Vice President Harris serving as the tiebreaking vote in her new role as president of the the Senate.
Harris administered the oath of office to Raphael Warnock and Jon Ossoff hours after her own swearing-in.
The pair of Democratic victories in the Jan. 5 Senate runoff elections gave the party control of both the White House and Congress, with the thinnest of majorities in the upper chamber.
Harris also swore in Democrat Alex Padilla, the former California secretary of state, to fill Harris' own Senate seat. He was appointed by California Gov. Gavin Newsom, a Democrat.
"The chair lays before the Senate ... a certificate of appointment to fill the vacancy created by the resignation of former Sen. Kamala D. Harris of California," she said, laughing, before adding, "Yeah, that was very weird."
With the new senators' swearing-in complete, Sen. Chuck Schumer, D-N.Y., becomes the Senate majority leader and Sen. Mitch McConnell, R-Ky., the minority leader. Sen. Patrick Leahy, D-Vt. , became the new president pro tempore of the Senate, placing him third in the line of succession to the presidency. He previously held this position from 2012 to 2015.
Details of a power-sharing agreement are still being developed by Schumer and McConnell to lay out practical issues about the chamber's operations going forward.
A Democratic majority, however narrow, will enable the party to set the chamber's legislative agenda and make it easier to confirm President Biden's Cabinet picks.
Georgia's Secretary of State's office certified the results of the runoff elections the day before Biden's inauguration.
Biden was the first Democratic presidential candidate to win Georgia since 1992. Ossoff and Warnock's wins were also history-making. Ossoff is the state's first Jewish senator and Warnock is Georgia's first Black senator and the first Black Democratic senator from the South.
Padilla's appointment is also historic: He is the first Latino to represent California in the U.S. Senate.