Boro boss Aitor Karanka confirmed after Saturday's FA Cup loss to Hull City that he was closing in on Omeruo, and now he has finalised a deal.
The 20-year-old, who can play at centre-back and full-back, is yet to make his debut for Chelsea but he has 14 caps for Nigeria.
"Kenneth is a strong defender and I think we need to improve in this area," said Karanka.
"I know him Jose (Mourinho) and has told me about him and I think he's going to be very good for us to add to the squad."
Omeruo is now set to go straight into Boro's squad for this weekend's clash at Blackpool.
Young Kenneth has very large legs, almost proportionally frog-like.- Petulant_Radish