The Dutch defender will replace Arsenal-bound Mathieu Debuchy and has put pen to paper on a six-year deal at St. James' Park to become the club's sixth summer signing.
The 24-year-old has signed a six-year deal at St. James' Park in a deal that is reported to be worth 7.5 million euros.
The right back will act as a replacement to Mathieu Debuchy, who has left the Magpies for Arsenal, and becomes Alan Pardew's sixth signing of the summer.
Janmaat was influential in Louis van Gaal's side's run to the semifinals of the World Cup in Brazil as he took his tally of international caps to 21 with five appearances in South America.
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His call-up followed an impressive campaign in Eredivisie for the Rotterdam-based club, for which he made 74 appearances across two seasons, scoring five goals.
Speaking on his arrival in the North East, he said he was looking forward to sampling the famous atmosphere inside the Magpies' home ground.
"Newcastle is a fantastic club, with a big history and a great stadium. I have also been told all about how great the fans are," he told the club's website. "This is the perfect move for me, and I am really looking forward to being with the team and getting started here at Newcastle. I think we are going to have a great season."
Pardew, meanwhile, revealed that Janmaat will offer plenty at both ends of the pitch as his side looks to improve on a 10th-place finish in the 2013-14 Premier League table.
"We are delighted to bring Daryl to the club," he said. "He is the perfect example of a modern fullback; someone who is good defensively but offers a real threat going forward as well. Daryl had an excellent World Cup and we are looking forward to him continuing that form for Newcastle."
Janmaat follows Ayoze Perez, Jack Colback, Siem de Jong, Remy Cabella and Emmanuel Riviere to the club in what is proving to be a busy summer for the Tyneside outfit.