Free-agent Smith most recently played for Maidenhead United where he won the National League South and counts Wealdstone his 19th club he has represented.
After signing for the Stones, the 30-year-old said he joined with only one aim for this season.
"This transfer has been a long time coming as I nearly joined in the summer," he told the club's website.
"The challenge is there to push on and gain promotion. Having done so before and with my experience, I believe I can help what already is a good squad of players."
The Stones have been going well this season, already sitting in a play-off place and boss Bobby Wilkinson said he was glad to finally get this one over line.
He said: “Christian is a commanding centre midfielder who is a great addition and can contribute a lot to our fantastic group of players. I’m thrilled to have got him in.”
Smith could make his first appearance against Concord Rangers in the FA Trophy this weekend.