Virginia Del. Bob Marshall (R) will run for retiring Rep. Frank WolfFrank WolfHouse votes to mandate sexual harassment training for members and staff Trump, global religious freedom needs US ambassador to lead Bottom Line MORE's (R-Va.) northern Virginia seat, he tells a local conservative blog, adding uncertainty to what's becoming a crowded Republican field.

Marshall is best known for his socially conservative activism. He has led the charge to keep gay marriage illegal in Virginia, and wrote the law banning partial-birth abortion in the state. He unsuccessfully sought the GOP nomination for Senate in both 2008 and 2012. 

He's also made some statements that have stirred controversy, declaring in 2012 that "sodomy is not a civil right."

Marshall will face Virginia Del. Barbara ComstockBarbara Jean ComstockHouse Republican backs bill to overhaul DC Metro Poll: Voters in vulnerable GOP districts oppose tax bill Giffords targets 8 Republicans on conceal and carry in new ads MORE (R), a well-connected beltway power player and former Wolf staffer, and longtime Republican operative Rob Wasinger (R), who was Rep. Kerry Bentivolio's (R-Mich.) chief of staff until he resigned to run for the seat last week.

Comstock is the favorite for the nomination — she's already locked some big-name endorsements including the backing of Mitt Romney and conservative radio star Mark Levin, and raised $300,000 for the race in just one month. Marshall's decision to run may actually make things easier for her, as he and Wasinger may split the anti-Comstock conservative vote.

Democrats are hopeful they can compete for the slightly Republican-leaning seat, and have opted to avoid a primary and use a nominating convention to help the eventual nominee save money.