The 19-year-old made his first team debut for Spurs during a 5-0 English Premier League win over Southampton on December 15, and has since been rewarded with a new contract running until summer 2029.
He was most recently an unused substitute as Spurs were taken to extra-time by Tamworth in the FA Cup last weekend.
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Explaining his decision to join Aberdeen, the highly-rated centre-back said: "I think about a week ago my agent called me and said 'Aberdeen'. Obviously I know that it's a big club, got a big support, passionate supporters, and I know about the history about the club. That made it a no-brainer to come here.
"Then as soon as I found out what the manager wants from me, what he wants me to do, how he wants the team to play, it suits my style quite well. I was just thinking that's a no-brainer.
"I have done my research and saw that James Maddison came here. The impact that he had was amazing. I have seen the goal that he scored against Rangers. It was a big performance and it was a big stepping stone for him. It put his name on the map. It gave him the platform to perform at the highest level."
Asked to describe his best attributes, Dorrington added: "I'd say my heading because I'm quite tall. My pace, so defending the ball in behind really or even with the ball, stepping out and dribbling with the ball through midfield.
"I'd say on the ball I'm quite good with the ball as well with my range of passing and breaking the lines."
Commenting on his latest recruit, Aberdeen boss Thelin said: “Alfie is a really exciting young prospect who recently made his debut for the Tottenham Hotspur first team.
“He has good speed, stature and good ability on the ball and his arrival will further strengthen our options at centre-back.
“We believe this will be an environment in which he can continue to grow and gain some invaluable match experience in a really competitive league.”