Kamara joined Boro on deadline day in a move from MLS side Sporting Kansas City, but having also been on international duty with Sierra Leone, he is only now heading back to Teesside.
He was waiting on paperwork, which he has now received, and is set to be in contention to face Ipswich at Portman Road in the Championship on Saturday.
"Just collected my passport, work permit granted, so it's off to England in the morning," Kamara said via Twitter late on Wednesday.
"Whew. So very excited."