King joins on loan from Leicester until the end of the season.
He joined the Foxes as a youth in 2004 and since his first-team debut three years later has gone on to feature 379 times in all competitions.
King was part of the side that claimed a stunning Premier League title triumph in 2015-16 although he has fallen down the pecking order under Claude Puel.
"He is a talented and experienced midfielder who has competed in the Premier League and top end of the Championship with great success.
"I am sure he will have a positive impact on the squad for the rest of the season."