Leicester sign ex-England full-back Brown on short-term deal
The 37-year-old former Harlequins stalwart joined Newcastle in 2021.
But he has been without a club since the Falcons decided against taking up the option of an extra year in his contract during pre-season.
"I still believe I have a part to play in the game," Brown told Leicester's website. "I didn't believe it was my time to stop because I still feel good."
Tigers head coach Richard Wigglesworth said: "Mike is an experienced Premiership player, who has represented his country and won trophies at club and Test level."
Wigglesworth, a former England scrum-half, added: "His experience and his knowledge is vital during this Six Nations period where we have a number of players away. Mike is hungry to prove himself."
Brown, who won two Premiership titles with Quins and three Six Nations championships with England, said he was delighted by the chance to turn out for the Tigers.
"When Leicester Tigers offer you the chance, it is a hard one to turn down," he said. "It has been really good out on the field with this group."