Republicans and Democrats are quickly lining up candidates to replace Virginia Del. Barbara J. Comstock in a special election scheduled for January, when she will move on to her new seat in Congress.

Kathleen Murphy, who lost narrowly to Comstock in 2013, is seeking the Democratic nomination for Comstock’s McLean-based seat in the Virginia House of Delegates.

On the Republican side, McLean consultant Allen Johnson, who served as an agricultural trade ambassador in the George W. Bush administration, has announced his candidacy. So has Craig Parisot, who has worked in the technology field and for local nonprofit organizations.

Both parties will pick their nominees on Saturday, although Murphy, a McLean consultant and former Clinton administration official, announced her candidacy Monday with the support of Gov. Terry McAuliffe and a long list of other prominent state and local Democrats.

A special election will be held Jan. 6 to replace Comstock, who won handily in the open race for Virginia’s 10th Congressional District last week.

“It is important that the people of the 34th District have the opportunity to elect representation prior to the start of the 2015 session,” Virginia House Speaker William J. Howell said Monday in announcing the election.

Republicans will hold a firehouse primary (a canvass held by the state party) from 10 a.m. to 2 p.m. Democrats have scheduled a similar unassembled caucus from noon to 4 p.m. Party officials say Murphy is unlikely to face a primary challenger. If no other candidate files by the Wednesday deadline, the party may cancel the caucus.

The 34th District, which covers parts of Fairfax and Loudoun counties, is more Democratic than the congressional seat Comstock won on Nov. 4. Murphy lost last year by just 422 votes out of nearly 30,000 cast, and all three statewide Democratic candidates won the district that year.

However, former governor Robert F. McDonnell (R) won there in 2009, and the seat became more Republican after redistricting in 2011. President Obama and Republican Mitt Romney split these suburban and exurban voters in the 2012 presidential election. Democrats have tried and failed to unseat Comstock, a prodigious fundraiser with powerful Republican Party connections, in every election since she took office in 2009.

The 2013 race between Comstock and Murphy turned nasty, with their mutual dislike evident in public appearances. Comstock called Murphy “the Leona Helmsley of Virginia” over taxes paid late on property she co-owned with her husband as well as unpaid taxes on a home in New York owned by her ex-husband.

The two also sparred over Comstock’s vote for a 2013 law that imposed strict new requirements on clinics providing abortions. Democrats accused Republicans of trying to force clinics that couldn’t comply out of business. Murphy went further by saying that the measure could deny services to cancer patients by affecting facilities that provide screenings. In response, Comstock claimed that Murphy had lied to cancer patients.

“That disturbed me,” Murphy said later, because “I’m a cancer survivor.” A Comstock spokeswoman responded that Murphy “sadly has been very bitter and not gotten over her loss.”