McNair has experience in the top-flight having played under Louis Van Gaal for his boyhood club, he will bring competition to the Brighton midfield after the departure of veteran Steve Sidwell.
Brighton's initial bid rejected by the Black Cats
Brighton boss Chris Hughton is reportedly looking to strengthen his midfield, which currently consists of the likes of Beram Kayal, Dale Stephens, and Davy Pröpper.
Following a successful promotion campaign with Fulham, Oliver Norwood's return from his loan spell will provide Hughton with further options in midfield as he looks to cement the Albion's top-flight status for years to come.
McNair is young and has good experience with Sunderland in the EFL Championship, having made 18 appearances last season. For Manchester United, the Northern Irishman made 24 appearances as he broke through the ranks in the 2014/15 season.
McNair is adept at playing at centre-half, at fullback, and as a deep holding midfielder as well. Such versatility will be useful for Hughton in those periods of the season when the games are coming thick and fast.
Brighton have also been linked with another defender in Reading's Liam Moore, although no official bid has been submitted by the Seagulls. It has been an impressive summer for the Seagulls already with these early deals, Hughton's side look well set for another campaign of solidity in the Premier League.