Kieran Trippier has joined Newcastle from Atletico Madrid for an undisclosed fee.
The England right-back, 31, is the first signing the Magpies have made since they were taken over by Saudi-backed owners in October.
After the relegation battlers confirmed the news, 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, and having worked with Eddie Howe before [at Burnley], 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 the 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.
"It's a good team, good manager, good staff. I fight for everything and I'll be fighting for Newcastle now.
"I know the position they're in but I want to help the team on and off the pitch with my experience to climb up the table. I'm not shy to get in a battle.
"I'll give 110% on the training pitch and put that into the matches. It's a huge club and the project that's happening now is very exciting.
"It's a great opportunity for me and my family. It's an honour for me to be here."
Trippier has signed a two-and-a-half year deal at St James' Park.
The former Tottenham man lifted the LaLiga title under Diego Simeone last season and has won 35 caps for the Three Lions.
Newcastle are currently just one point above rock-bottom Norwich and more signings are expected to follow Trippier during the January sales.
Speaking on Twitter, the defender added: "I’m so happy to be joining Newcastle.
"Everyone knows the fans are unbelievably passionate and I will give my absolute all for them.
"I can’t wait to get to work. Thank you to everyone at Newcastle and the fans for the very warm welcome I have received so far."