Republican Winsome E. Sears will play a critically important role in the next four years as Virginia’s lieutenant governor.

The former Marine who served one term in the Virginia House of Delegates is the first woman and first woman of color elected to the state’s second highest office. In that role, she will be next in line to run the state should the governor die or become incapacitated.

She also will preside over the state Senate, a 40-member body that remains in Democratic control with a 21-19 split between Democrats and Republicans.

Following Tuesday’s GOP sweep of the state’s top offices and the House of Delegates, Democrats view the state Senate as the last bastion of protection against highly conservative Republican measures on highly controversial issues, including abortion rights, that are likely to come before the body beginning with January’s General Assembly session.

However, if just a single Democrat breaks rank to join the Republicans in a vote, the newly elected GOP lieutenant governor would cast the powerful tie-breaking vote.

Virginia’s current lieutenant governor, Democrat Justin E. Fairfax, used that power more than 50 times, including casting the tie-breaking vote to expand Medicaid in Virginia, increase the state’s minimum wage, legalize marijuana and marriage equality.

Ms. Sears, a 57-year-old businesswoman who came to the United States at age 6 with her family from Jamaica,

campaigned on a conservative platform of supporting gun rights, which earned her an endorsement from the National Rifle Association; opposing abortion; backing vouchers for school choice and creation of charter schools; and protecting Virginia’s controversial “right to work” laws, while opposing unionization.

Her message won over a majority of voters. According to the state Department of Elections’ unofficial returns, Ms. Sears won 50.99 percent of the votes, or 1.65 million votes, to defeat Democratic Delegate Hala S. Ayala, who received 48.9 percent of the vote, or 1.58 million votes.

Delegate Ayala, a former cyberse- curity specialist with the U.S. Coast Guard who identifies as an Afro-Latina, used her own background as a former single mother struggling to make ends meet in a minimum wage job as a gas station cashier to push a platform of broader access to health care, women’s rights an gun safety.

In a concession statement, Delegate Ayala congratulated Ms. Sears “on making history and paving the way for future women leaders who look like us.”

“We may not be able to claim victory today,” she said, “but we know that the results of this election are simply a minor setback in our larger fight for progress.”

In a victory statement on Wednesday, Ms. Sears said, the work of the state is too important to be stopped by divisions.

“There are some who want to divide, but we must not let that happen,” Ms. Sears said.

“What we are going to do now is be about the business of the Commonwealth. We have things to tend to. We are going to fully fund our historically Black colleges and universities. We’re going to have safer neighborhoods, safer communities and our children are going to get a good education.”