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 arrives at St. James' Park having spent a successful two-and-a-half-year spell in Spain, culminating in La Liga triumph last season as Atlético pipped rivals Real Madrid to the Spanish title.
He rejoins Eddie Howe after being signed by the Magpies' head coach in 2011 during his time at Burnley. Trippier 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."
Newcastle United head coach Eddie Howe 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."
Born in Bury, Greater Manchester, Trippier began his career at nearby Manchester City and made his first steps into senior football with loan spells at Barnsley and Eddie Howe's Burnley.
His loan spell with the Clarets was turned into a permanent switch in January 2012 and he helped the club to reach the Premier League in 2014, eventually clocking up four years at Turf Moor.
After becoming an established defender in the top flight, he completed a move to Tottenham Hotspur in summer 2015 and would go on to play Champions League football, as well as making his senior debut for England against France in June 2017 - the first of 35 international caps.
In July 2019, he made a high-profile switch to Diego Simeone's Atlético Madrid, becoming the club’s first English player in 95 years and making 28 league appearances last season as Atlético became Spanish champions.
He ended the 2020/21 campaign by starting for England in the UEFA European Championship final at Wembley as Gareth Southgate's Three Lions narrowly lost to Italy.
