Jawara follows former team-mates Lamin Manneh and Shea Thompson-Harris in joining the Millers.
He was previously part of the Notts County youth setup, featuring for their U19s.
"I'm delighted to get Mussa on board," Millers joint-manager Mark Harvey said.
"He did excellently against us in a trial match in early May and caught my eye. He followed that up Saturday against Sandiacre with a couple of goals.
"Strong and pacey with a great attitude, we have high hopes for this lad."
Photo credit: Carlton Town
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