The 31-year-old full-back has moved back to the Premier League for an undisclosed fee, understood to be in the region of £12million plus add-ons.
The former Tottenham defender has signed a two-and-a-half-year contract and his arrival signals the launch of a new era under the Magpies' Saudi-backed owners.
A club statement said: "Newcastle United are delighted to confirm the signing of England full-back Kieran Trippier from Atletico Madrid for an undisclosed fee.
"The 31-year-old has agreed terms on a two-and-a-half-year deal and becomes the first senior signing under the club's owners and head coach Eddie Howe."
Trippier, who was signed by Howe for former club Burnley during his spell in charge at Turf Moor, won LaLiga with Atletico last season but is relishing his return to England.
He said: "I'm delighted to be joining this fantastic club. I really enjoyed my time in Madrid, but when I became aware of interest from Newcastle United, and having worked with Eddie Howe before, I knew this was where I wanted to be.
"I'm aware there is a lot of work ahead of us, but I know the demands of Premier League well and I know what an amazing club this is with very talented players. I can't wait to get started and I'm excited to step out at St James' Park as a Newcastle player."
The Bury-born full-back finds himself pitched into a top-flight survival battle with Newcastle, who entertain League One Cambridge in the FA Cup third round on Saturday.
The Magpies sit just one place off the foot of the Premier League table and Howe will hope this is the first of a series of new recruits to help in that fight.
The head coach said: "I am really pleased to welcome Kieran to Newcastle United. I have long admired his abilities and have followed his career, so when the opportunity arose to secure him, we didn't hesitate.
"A lot of hard work has gone into planning for the January transfer window long before the month began, which is clear in how quickly we have been able to complete this move.
"I would like to thank everyone involved, particularly our owners, and I'm very much looking forward to working with Kieran again on the training pitch."