The Bluebirds formally unveiled the 21-year-old at their Vale of Glamorgan base on Friday, having paid an £8million fee to bring in the England international on a four-year contract.
The move is a real coup for Mackay with Caulker having made 28 appearances in all competitions for Spurs last season, catching the eye of England boss Roy Hodgson in the process.
Caulker, for his part, felt he needed to establish himself as a first-choice Premier League centre-half to provide the best possible chance of selection for next year's World Cup, and Mackay admires the attitude of his latest acquisition.
The Scot said: "To be part of a squad is a very good thing and at the time you are loathed to leave because it has a comfort blanket associated with it.
"You are wrapped in it, you have been there and you know it. To actually step out and go and further your career is a brave decision.
"It is something that I would commend players for when they do it. You see a situation in football when they leave a club and it is unexpected. When it is for the reasons of playing football regularly then I think that is a brave decision. It shows that a player has maturity attached to them and where they see their career going.
"People will be surprised that Steven left Tottenham, but I have a great deal of time for the fact that he wanted to come here to play football and further his career.
"We will aim make him as good a player as he possibly can be and we are very impressed by the way he was so determined to leave his comfort zone."
Mackay has already added Andreas Cornelius, John Brayford and Simon Moore to his squad this summer, and he remains hopeful of adding a few more faces before the transfer window shuts.
Cardiff have had a bid of around £9.5million accepted for Toulouse's France midfielder Etienne Capoue, with Mackay hopeful of convincing the 25-year-old to make the switch to the Premier League.
The Bluebirds have also been linked with West Brom striker Peter Odemwingie and Espanyol defender Hector Moreno.
"We saw last year that near the end of the window we brought in five or six," said Mackay.
"It is really about when they fall; we have got irons in the fire at the moment and targets.
"Sometimes it is not just about when it suits you when a transfer is done. We will be diligent and will go about our work professionally, the way we always go about trying to bring players in.
"There are still targets out there and are still people I want to bring into the club."
Click here for completely free £10 bet with Sky Bet