A breakthrough in talks on Friday evening has seen United end up paying substantially less than the £100m-plus price Brighton were quoting for the 22-year-old last summer.
The Old Trafford club will pay Brighton an initial £65m for the 22-year-old, with a further £5m available in add-ons, taking the total package to as much as £70m. The Seagulls have also secured a sell-on clause.
Baleba is now free to complete his medical with United this weekend.
Manager Michael Carrick moved for Baleba this week after identifying a need to add further depth in midfield, following the earlier signings of Andrey Santos from Chelsea and Youri Tielemans from Aston Villa. Once completed, the deal will take United's summer outlay to £153m, though it still represents a significant saving on the fee Brighton were demanding when a move was last discussed around the 2025 deadline.
Baleba joined Brighton from Lille in 2023 and has made 92 Premier League appearances for the south-coast club, but he is currently working his way back from an ankle injury sustained during their pre-season training camp in Austria.
His arrival ends Manchester United's search for midfield reinforcements following the departure of Casemiro after his contract expired, while Manuel Ugarte's expected exit was put on hold after the Uruguayan suffered a serious knee injury on World Cup duty.
Brighton, meanwhile, have already lost several key figures this summer, including Jan Paul van Hecke to Tottenham and Danny Welbeck to Chelsea, as they continue to cash in on players developed under their recruitment model — Baleba's fee falls well short of the club-record £115m they received from Chelsea for Moises Caicedo in 2023.
It remains to be seen whether Carrick will also pursue cover at left-back to challenge Luke Shaw, or whether Baleba — a left-footed player who has featured in that position on occasion — can provide an alternative alongside regular right-backs Diogo Dalot and Noussair Mazraoui, both of whom have also been used on the left.
Santos, Tielemans and England international Kobbie Mainoo will all be available when United travel to newly promoted Hull City for Saturday's lunchtime kick-off, though Baleba himself is unlikely to feature again until his fitness is fully restored.