The 20-year-old centre-back is yet to make a first-team bow for the Wearside outfit but is highly-rated at the Stadium of Light where he has become a regular in the under-23s side.
Consett-born Ledger enhanced his growing reputation with a successful spell on loan with Norwegian Tippeligaen side Viking Stavanger at the end of last term, during which he made fifteen appearances in all competitions.
Harrison has been keen to bring in defensive reinforcements, with Louis Laing out for a fortnight with hamstring trouble, Scott Harrison nursing a foot injury and Liam Donnelly away with Northern Ireland’s under-21s this week.
Ledger, who has been on the books at Sunderland since he was 8, has now penned a loan deal to keep him with Pools until the end of the season and is the second new signing in a week after fellow defender Keith Watson arrived from St Johnstone last Thursday.
He will go straight in to contention for Saturday’s game against Maidstone United.