The 27-year-old joins the Magpies from Southampton, where he spent the 2024/25 campaign after making the switch from Arsenal last summer.
Ramsdale brings a wealth of Premier League experience to St James' Park, having made 183 appearances and kept 41 clean sheets in the competition. His top-flight journey began under Eddie Howe - now Newcastle manager - when he made his Premier League debut for AFC Bournemouth in 2019.
The English goalkeeper began his professional career at Sheffield United before moving to Bournemouth, and then returning to the Blades.
A subsequent transfer to Arsenal saw Ramsdale rise to prominence, particularly during the 2022/23 season when he played a key role in helping the Gunners finish second in the Premier League.
His impressive performances that season earned him a senior England debut and a place in Gareth Southgate's squad for the 2022 FIFA World Cup in Qatar.
"It's great to be here. I've always loved coming here and I've seen how passionate and loud the fans can be," said Ramsdale.
"I've always loved playing here at St. James' Park - I've not always had the greatest of results, but when the fans get behind you it's some place.
"Coming to the stadium and seeing it empty today, it's quite surreal to think that this is going to be home for the foreseeable future. I've got the kit on, it's got the nice Champions League badge on the sleeve and I'm delighted to be here.
"Working with the manager and his coaching staff again were a big draw for me. They've already had a great influence on my career and the gaffer turned me from a man into a professional footballer at Bournemouth.
"He really showed me the ropes so the manager and his coaching staff were a huge selling point for me to come here."