Loudoun County Democrats announced Monday that Mary Daniel, a lawyer from Berryville, will replace Kathee Myers as the Democratic nominee for the 33rd District House of Delegates seat.

Daniel will face Republican challenger David LaRock, a hard-line conservative newcomer who defeated the more moderate 20-year incumbent Del. Joe T. May in an upset in the June 11 primary.

Despite May’s widespread name recognition after 10 terms in office, LaRock won a decisive majority of the vote — 57 percent, according to unofficial election results — after a contentious primary race.

Myers, who had been announced as the Democratic nominee this month, said in a statement that she had filed for candidacy in the race to provide an alternative for voters. There had previously been no Democrat or independent candidate slated to run in the general election against the winner of the Republican primary.

“I was determined to ensure that the issues that are important to this district are addressed and that people have a real choice in this election,” Myers said, adding that the campaign quickly proved to be unmanageable.

“It is a much larger undertaking than what I expected, and I am currently unable to devote the time necessary to ensure that we turn HD 33 blue,” she said.

Daniel, who told The Washington Post on Friday that she had filed for candidacy with the State Board of Elections, said she had at first been hesitant to enter the race because of her respect for May. But she “found herself called to action” after May’s loss to LaRock, a Democratic committee statement said.

“Joe May is a decent and honorable man who put his constituents and his duty first, and politics second,” Daniel said. “Our area has lost a capable advocate in Richmond.”

Daniel, who describes herself as a moderate, said she hopes to lead as May did: by representing a wide range of constituents in the district, including moderate Republicans, Democrats and independents.

“The reasonable, moderate majority in our area deserves a representative who shares their values,” she said.

Daniel, a native of Frederick County, is president and managing attorney of the Daniel Group, a Winchester-based law firm. Before founding her firm in 1998, Daniel spent more than five years working with the Office of the Commonwealth’s Attorney in Winchester, where she prosecuted domestic violence and sexual assault cases. She has one daughter with her husband, William Daniel, an administrator with the Frederick County public schools.

Daniel said she is a fiscal conservative, a “mainstream moderate and an experienced problem-solver.”

But Daniel’s plans to follow in May’s footsteps will not help voters who disapproved of May’s fiscal policies, according to LaRock. He said he thought that May’s vote in favor of a landmark transportation funding bill passed by the General Assembly was a deciding factor in the primary election: The legislation would pay for transportation needs across the state by raising taxes, a measure that many voters said they could ill afford, LaRock said.

“Taxes are too high in Virginia, and we need to do a better job of prioritizing spending so we can lower taxes and spending, and cut excessive regulation to provide a climate for job creation and economic growth,” he said in a statement. “Democrat Mary Daniel will not deliver the results we need. The people of the 33rd District want their state government to provide high-quality essential services like education and transportation in an efficient and responsible manner, and I plan to fight to those ends.”

LaRock said the “large turnout” in the primary — and the fact that the district supported Mitt Romney in the 2012 presidential election by 14 points — proved that voters supported the conservative message of LaRock’s campaign.

About 9 percent of registered voters in the 33rd District voted in the June 22 Republican primary, according to election officials. More than 5,100 voters cast ballots in the race across Loudoun, Clarke and Frederick counties, and about 750 votes separated the two candidates, according to unofficial election results.

Loudoun Democratic Committee Chairman Evan Macbeth said he understood Myers’ s decision to leave the race and was enthusiastic about Daniel’s candidacy.

“Democrats are committed to ensuring that every voter in the commonwealth has representation in Richmond that reflects our shared values and Virginia common sense,” he said in the Democratic committee statement.

Daniel will challenge “the narrow, divisive vision of Dave LaRock, Ken Cuccinelli and Virginia’s Republican Party,” Macbeth said.