Hooper, 22, signed for the Scottish Premier League side on Tuesday morning after a summer of speculation linking him with a departure from Scunthorpe United.
Iron fans always expected him to go, and it became clear when he was left out of the squad for Saturday's pre-season friendly against Sheffield Wednesday that he had his heart set on a move.
Celtic are believed to have paid £2.4million for the English forward, who was signed from Southend United for just £175,000 two years ago.
Middlesbrough were heavily linked and initially installed as favourites to sign him, but Lennon revealed he was also competing against the lure of the richest league in the world.
"It was interesting because, when you get men of the calibre of [Middlesbrough manager] Gordon Strachan after him, and there were a few other clubs showing interest including West Ham and Blackpool, who can offer Premiership football, to get him in the end is very, very satisfying," said Lennon.
"That's because we have done a lot of work on this one.We've had an eye on him for a while. He's young, but I think he is ready. I like the way he plays the game. He is a hungry boy, and the hungrier we have, the better."