The youngsters, both 20, have made a huge impact since breaking through earlier this season.
Our director of football David Pleat revealed: "Both have made good progress this season.
"Their opportunities have come from injuries, whatever, but they have proved they can handle the senior team, which is a massive bonus to the manager.
"Obviously, that doesn't mean necessarily they are going to stay at such a high level consistently but they have made a point, proved a point and as such, it is very unfair to treat them as very junior professionals and they were getting very junior professional salaries.
"We've given them contracts which are more in line with players who have emerged through the ranks.
"They are extended contracts. Neither players' contracts were expiring at the end of this season and that is the act of good faith we have showed to them."
King and Thelwell were handed the chance to shine against Liverpool in November. Both grabbed the chance and King has remained a regular in the first team since. Thelwell has stayed in and around the squad and has also won his first England Under-21 cap.
Listen to what David had to say by clicking here
Ledley King and Alton Thelwell have signed new, extended contracts at Spurs Lodge this afternoon (Friday).