The 20-year-old spent the second half of last season on loan at The Riverside, and he become an important memeber of Karanka's squad.
Now despite interest from around Europe and the Premier League, Karanka has been able to persuade his old boss Jose Mourinho to send Omeruo back to Boro for a full campaign.
“The most important thing is he is happy to join us. He is the kind of player who is very important on the pitch and off the pitch," said Karanka.
“He’s always ready to train, always ready to have fun, always joking.
"He is a player everybody loves; his team-mates, the staff, the supporters, everybody in the club and the town love him.”
Omeruo is now set to link-up with Boro having spent the summer playing for Nigeria at the World Cup finals.