The Black Cats, who had tied up the Scotland international on a season-long switch from parent club Reading in the summer, had been refusing to free him up despite the fact he has made only seven starts this term.
But, frustrated by that paucity of game time, and aware of Hibs’ interest, the player’s representatives applied pressure on the current Sunderland boss Phil Parkinson.
Late last night, with a couple of forward options lined up to move to the Stadium of Light, he finally relented and, with terms already agreed between Reading, Hibs and McNulty, the local lad is now set to reunite with his former boss, Jack Ross, in Leith, until the end of the current campaign.
Ross had taken McNulty to the English League One side prior to his sacking in October and is a fan of the 27-year-old, who spent the second half of last season on loan at Hibs, where his form helped the Easter Road outfit finish ahead of city rivals Hearts.
His performances in green and white also earned the former Coventry City forward his first Scotland cap.
This will be McNulty’s third spell at the club that released him as a teenager and he follows former team-mate Stephane Omeonga and St Mirren’s Paul McGinn in the door as Ross prepares his squad, which is currently sitting sixth in the league, for a push up the table.
He is not expected to be the club’s final transfer dealing of the day and his return could signal Florian Kamberi’s loan switch to Rangers.
The 24 year old Swiss player has been targeted by Steven Gerrard as he attempts to bolster his attacking options following the midweek calf injury to veteran striker Jermain Defoe.