Levin's nod gives Comstock a boost with the conservative base against what could be a crowded GOP field.
He said he has known and worked with Comstock for more than two decades and wanted to "endorse her wholeheartedly."
"And I'm not the only conservative who is going to endorse her," he added.
Comstock, a former Wolf staffer who has been active in both state and national party politics for decades, is the establishment favorite to succeed Wolf in the slightly Republican-leaning district.
Virginia state Sen. Dick Black (R) is also running and has some support from religious conservative and Tea Party activists, as well as a history of controversial remarks. A half-dozen other Republicans are seriously weighing runs for the seat.
Local Republicans have yet to decide whether to select their nominee in an open primary or a convention. The latter setting could give an advantage to a conservative candidate.
Levin isn't the only big Republican name to support Comstock. Mitt Romney, who Comstock worked hard to elect president, tweeted an endorsement shortly after she announced her bid earlier this week.