Andover Democrat Dan Koh, the second-place finisher by 52 votes in the Third Congressional District, will officially file for a recount on Friday, his campaign said.
"We want the process to progress as swiftly as possible so that the ultimate nominee will have adequate time and resources to win in November," the Koh campaign said in a Friday morning statement.
The deadline to file for a recount is 5 p.m.
Lori Trahan of Westford claimed victory Tuesday evening in the 10-way Democratic primary, and reiterated her confidence in the results on Wednesday.
Associated Press numbers show Trahan landed at the top of the pack with 18,368 votes, narrowly edging out Koh's 18,316. The third-place finisher, Lawrence state Rep. Juana Matias, netted 12,914 votes.
Secretary of State William Galvin on Wednesday ordered all ballots and election paperwork for the race be impounded in case a recount became necessary.
Koh had worked as Boston Mayor Marty Walsh's chief of staff and Trahan was chief of staff for former Congressman Marty Meehan, now president of UMass.
The ultimate winner in the race will face Republican nominee Rick Green and unenrolled candidate Michael Mullin.
A candidate must file the signatures of 500 Democrats with local elections officials to seek a recount. Both the Trahan and Koh campaigns said Thursday they had begun the signature-gathering process.