The 41-year-old will be installed at Broadhurst Park on Monday after he has taken charge of Brig's NPL Premier Division encounter against Basford United at the Sir Tom Finney Stadium on Saturday.
As exclusively revealed by the Lancashire Post, the Red Rebels first made an approach for Reynolds just over two weeks ago following Brig's thumping 6-1 victory over Stafford Rangers.
Initially, they were thwarted in their pursuit with the Board at Irongate determined to hang on to their bright young manager, who had only recently signed a new three year contract in May.
However, it became clear that the fiercely ambitious Reynolds was keen to take on the job, with FC United a division higher in the football pyramid and averaging regular four-figure crowds for home games.
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The two clubs have finally reached an agreement over compensation which will release Reynolds from his contract.
The Brig boss has served the club for many years as a player before becoming previous boss Neil Crowe's assistant in 2012.
He took over from Crowe in December 2017 and has led the club through a golden period in its history.
Within six months, he guided the club to their first piece of silverware in more than a decade when they claimed the NPL League Cup, beating Grantham Town 2-1 in the final at Leek Town's Harrison Park.
Last season, his first full campaign in charge, Brig - with one of the lowest budgets in the NPL First Division North - achieved promotion to the Premier Division via the play-offs, beating Prescot Cables 1-0 thanks to Chris Marlow's late winner.
The club has made a decent start to life at the higher level, picking up 17 points from their first 12 games.
In a prepared statement, Brig chairman Fran Doyle said: "During the past two weeks, there has been much speculation regarding the future of Bamber Bridge manager Neil Reynolds.
"The speculation arose following an approach by FC United of Manchester to become their manager.
"This approach was turned down by Bamber Bridge as Neil was under contract to this club.
"Discussions between Neil and both clubs continued and following the approval of a compensation agreement with FC United of Manchester, Bamber Bridge have reluctantly agreed to release Neil from his contract to this club.
"Neil has served Bamber Bridge as both a player and manager with great skill, dedication, integrity and passion for over two decades.
"Under Neil's management, the club has won the Integro League Cup and were promoted to the NPL Premier Division.
"Neil will take charge of his last match this Saturday at home to Basford United.
"On behalf of everyone at Bamber Bridge, we offer our thanks to Neil for everything he has done for this club and wish him every success for the future. Up the Brig."