The Black Cats have been linked with a move for the 22-year-old, who spent time on loan in the MLS at Toronto FC last year.
Lee Johnson has been on the lookout for a left-back to add to the ranks and has found someone he feels fits the bill in the shape of Gallacher.
Sunderland are moving quickly to secure his services and are expected to complete the deal for his signature on Wednesday.
Gallacher will link up with the League One side on loan and it remains to be seen if the deal will contain a purchase option for Sunderland to trigger if he impresses.
The Liverpool starlet will look to hit the ground running at the Stadium of Light as Johnson plots a promotion charge for the Black Cats.
Gallacher was taken to Merseyside by Liverpool from Scottish outfit Falkirk in the 2018 January transfer window and his senior debut came in 2019, in the EFL Cup against Aston Villa.
The defender will now look to clock up valuable senior game time at Sunderland, with the pressure on Johnson’s men to push for promotion.