Catherine Cortez Masto’s victory in Nevada clinched the chamber for Democrats.
The 2022 midterm elections shaped up to be some of the most consequential in the nation's recent history, with control of Congress at stake.
All 435 seats in the House and 35 of 100 seats in the Senate were on the ballot, as well as several influential gubernatorial elections in battleground states like Arizona, Georgia, Pennsylvania and Wisconsin.
Democrats were defending their narrow majorities in both chambers and retained control of the Senate, though control of the House isn't yet clear. But a Republican flip of the lower chamber would be enough to curtail most of President Joe Biden's legislative agenda and would likely result in investigations against his administration and even his family.
ABC News can project that Sen. Todd Young, R-Ind., and Sen. Tim Scott, R-S.C., will hold on to their Senate seats.
Their Democratic challengers are Thomas McDermott Jr. and state Rep. Krystle Matthews, respectively.
Vice President Kamala Harris spent part of her day on radio shows expressing support for Democratic candidates in key races in Wisconsin and Pennsylvania.
In a brief appearance on The Earl Ingram Show Tuesday morning, Harris pushed Wisconsin Gov. Tony Evers' reelection bid.
"He has cut taxes for working families. He's lowered costs for small businesses in Wisconsin in Milwaukee, and he must be reelected because he really does stand for our democracy and for freedom and equality," she said.
Harris also said electing Wisconsin Lt. Gov. Mandela Barnes to the Senate would play a crucial role in the president's ability to sign the John Lewis Voting Rights Advancement Act into law.
"It would be so important to put back teeth in the Voting Rights Act that folks marched and died for, and these are the things that are at stake," she said.
In another radio interview later in the day on Philadelphia's Evening WURDs, Harris urged voters in Pennsylvania to vote for Lt. Gov. John Fetterman for Senate, particularly as the Senate attempts to pass an assault weapons ban.
"Democrats understand the need to extend and to renew the assault weapons ban, and we need John Fetterman in the United States Senate to have the votes toward doing that," she said.
Harris also called on voters to elect state Attorney General Josh Shapiro as the governor of Pennsylvania "because people have a right to live in safe communities" and not be threatened by gun violence, she said.
-ABC News' Armando Tonatiuh Torres-García
What's the single most important issue among voters? Who do they trust to handle inflation? For ABC News' analysis of preliminary exit poll results, head here throughout the night.
Polling hours vary from state to state, and sometimes district to district within a state.
Here's a timeline of when the last polls close by state, all ET:
7 p.m.: Georgia, Indiana, Kentucky, South Carolina, Vermont, Virginia (polls close in some parts of Indiana and Kentucky at 6 p.m. ET)
7:30 p.m.: North Carolina, Ohio, West Virginia
8 p.m.: Alabama, Connecticut, Delaware, D.C., Florida, Illinois, Maine, Maryland, Massachusetts, Mississippi, Missouri, New Hampshire, New Jersey, Oklahoma, Rhode Island, Tennessee
8:30 p.m.: Arkansas
9 p.m.: Arizona, Colorado, Iowa, Kansas, Louisiana, Michigan, Minnesota, Nebraska, New Mexico, New York, North Dakota, South Dakota, Texas, Wisconsin, Wyoming
10 p.m.: Montana, Nevada, Pennsylvania, Utah
Polling location hours were extended from 8 p.m. to 10 p.m. in Luzerne County
11 p.m.: California, Idaho, Oregon, Washington
Midnight: Hawaii
1 a.m.: Alaska
