However the 30-year old forward, who was a free agent having left Middlesbrough in August, will not be eligible to play for the Ohio-based club until January 2015.
MLS rules mean he must sit out the rest of the regular season but he can train with Crew from next week.
"I'm very happy to be back in MLS with the Crew. I'm looking forward to next season," Kamara told BBC Sport.
"I hope I'm able to bring great success to the club that made me a professional soccer player in 2006."