April 4 (Reuters) - Wisconsin voters on Tuesday elected liberal Janet Protasiewicz to the state Supreme Court, flipping control to a liberal majority ahead of rulings on an abortion ban and other matters that could play a role in the 2024 presidential election.

Protasiewicz defeated conservative candidate Daniel Kelly in what New York University's Brennan Center for Justice called the most expensive judicial election in U.S. history. More than $42.3 million had been spent as of Monday, according to a WisPolitics.com review, far outstripping the previous record of $15.2 million.

In a major victory for abortion rights advocates, the result turns a court with a former 4-3 conservative majority to liberal control after 15 years, likely affecting a number of issues that have polarized Americans in other states such as voting rights and partisan control over drawing legislative maps.

But it was abortion that dominated the campaign, with the court expected in the coming months to decide whether to uphold the state's 1849 abortion ban.

That law took effect after the U.S. Supreme Court's decision last year to eliminate a nationwide right to abortion by reversing Roe v. Wade and granting individual states the authority to ban abortion.

With 75 percent of the ballots counted, Protasiewicz had 55.4 percent of the vote to 44.6 percent for Kelly, a lead of nearly 160,000 votes, according to the Associated Press.

The wide margin in a normally closely contested state suggests Democrats have continued to benefit politically from the Roe decision, which has brought motivated voters to the polls.

Protasiewicz put abortion at the center of her campaign, saying in one advertisement that she supports "a woman's freedom to make her own decision on abortion." Kelly, meanwhile, won the endorsement of anti-abortion groups.

"Tonight we celebrate this historic victory that has obviously reignited hope in so many of us," Protasiewicz told a victory celebration.Republicans also underperformed expectations last November in the first national elections since the court struck down Roe.

Kelly reluctantly conceded in an address to supporters, calling Protasiewicz an unworthy opponent who ran a "deceitful, dishonorable, despicable campaign."

But he added, "I respect the decision that the people of Wisconsin have made."

The election's outcome also holds major implications for the political future of the battleground state. Just as it did in 2020, the court could issue crucial voting decisions before and after the 2024 presidential election, when Wisconsin is again poised to be a vital swing state.

In addition, the court may revisit the state's congressional and legislative maps, which Republicans have drawn to maximize their political advantage.

While the election is technically nonpartisan, neither Protasiewicz nor Kelly made much effort to hide their ideological bent. The state Democratic and Republican parties poured resources into their favored campaigns, and outside organizations spent millions of dollars supporting their preferred candidate, including anti- and pro-abortion rights groups.

Democrats asserted a Kelly victory could have endangered democracy itself in Wisconsin, noting that a lawsuit from Republican Donald Trump challenging his presidential election loss to Democrat Joe Biden in 2020 came within one vote of succeeding at the court.

Reporting by Joseph Ax in New York and Daniel Trotta in Carlsbad, California; editing by Matthew Lewis, Stephen Coates and Gerry Doyle