The Parkhead club have confirmed the transfer - first revealed last week - has now been rubber-stamped after the 20-year-old Nigerian was granted a work permit.
The former PSV Eindhoven midfielder has signed a three-and-a-half year deal, and said: "I feel very happy and excited to be joining Celtic. I have wanted to join Celtic for a long time to develop myself."
He added: "They were interested in me in 2010 when I was with Sporting Lisbon.
"I don't know why that never happened but that was then and I'm happy now that I'm here at Celtic.
"The atmosphere here is great, and the people are great. They are always nice to me and encouraging me so I already feel at home.
"The players have made me feel welcome and happy. It's just like a big family here. They carry everybody along, and I'm happy with that.
"I'm delighted as Celtic are a big club - they like good players, produce good players and encourage and give the young players the opportunity to prove themselves and showcase their talents.
"I'm happy that I'm here and strongly believe that I will get the opportunity to prove myself and improve my game."