The 19-year-old was one of the Scottish Premiership side's best players last season.
Celtic's Erik Sviatchenko
Despite interest from elsewhere (via Daily Record), the 19-year-old decided to commit his immediate future to the Hoops by signing a long-term contract extension on Friday.
Kieran Tierney celebrates scoring for Celtic
And the centre-back is over the moon that his fellow defender has put pen to paper on the new deal.
"We all know the manager is keen in bringing young players up. For Celtic to sign Kieran Tierney for a five-year deal is massive," he told the Evening Times.
"It gives a good appreciation of how the work is going to be done in the future as well."
New Celtic manager Brendan Rodgers
Along with Leigh Griffiths, Tierney was arguably one of the few players in the Bhoys squad that showed both quality and consistency throughout the campaign.
And while there was plenty of optimism following Brendan Rodgers' appointment at Parkhead given his Premier League experience, much of that excitement would have evaporated had the youngster headed in the opposite direction and continued his development elsewhere.
He demonstrated last term that he is already one of the most reliable players in the squad, and his emergence is likely to send a message to those in the first-team that if they let their performance levels drop, they may well be a youngster waiting in the wings ready to take their place.