The 24-year-old joined on loan from Southend earlier in the season and has made five appearances for Neil Warnock's men so far.
The Whites announced Hall will pen a two-and-a-half-year deal in the new year to become the first permanent signing under the club's new owners GFH Capital.
Warnock told Leeds' official website: "When we brought Ryan in I said 'I believe he is a player with potential for a big future.'
"I'm sure during the length of his contract Ryan will have the opportunity to establish himself at this level, and you can see that from his contribution at Huddersfield a few weeks ago.
"It's not just experienced players we are looking for to add to the squad, and if we feel there are youngsters like him available at the right prices we will look to the future as well."