Ambrose, who has 14 caps for Nigeria, agreed a three-year contract with Neil Lennon's side and the 23-year-old admitted he had been tempted to Glasgow by the lure of Champions League action.
Celtic have been drawn in the same group as Barcelona, Benfica and Spartak Moscow.
"Today is one of the happiest days of my life, signing for one of the biggest clubs in the world - a club I have known about since I was young," Ambrose told Celtic's website.
"I have come here to find we are in the same group as Barcelona, Benfica and Spartak Moscow.
"It's a lovely group, you might call it the group of death and it will be hard, but hard work always pays.
"I am just looking forward to meeting my team-mates now, there is no better place for me than Scotland.
"I just can't wait to get started, to play in front of the fans and call this place home."
Source: AFP
Source: AFP