The result, coupled with Sunderland's success at Manchester United, meant the Welsh side were sent back to the Championship less than 12 months after they celebrated promotion to the top flight.
The opening goal arrived just 18 minutes in when Shola Ameobi scored only his second of the season.
Despite the home win, the St James' Park faithful spent much of the match calling for Alan Pardew to be sacked and the much-anticipated fan walk-out on 69 minutes - marking the last year they won a trophy in 1969 - saw a number of supporters leave the ground.
Whilst the protests continued, Cardiff pressed and the should have levelled, but brilliant goalkeeping from Tim Krul and last-ditch defending from captain Fabio Coloccini kept them at bay.
Newcastle then sealed victory with two goals in the last three minutes as Cardiff pushed forward in numbers.
The second arrived with just three minutes left as Loic Remy converted from close range and then Steven Taylor - on as substitute and making his 200th league appearance - hooked the ball home to seal the win and end Cardiff's stay in the Premier League as they find themselves back in the Championship.
It never looked like being a comfortable afternoon for Pardew whatever happened on the pitch and his side were fortunate not to be behind with just six minutes gone when Krul's weak punch fell to striker Fraizer Campbell on the edge of the box, and he steered his effort wastefully wide.
But it was opposite number David Marshall who kept his side in the game as the hosts hit back.
He produced two fine saves within seconds to keep out full-back Mathieu Debuchy's well-struck 16th-minute shot and then his bullet header from the resulting corner.
However, he was left helpless with 18 minutes gone when Moussa Sissoko crossed from the right for Ameobi, who had pulled away from marker Steven Caulker, to head firmly home.
Newcastle looked as if they might run riot, with Sissoko seeing a shot and then a cross deflected against the woodwork, while Cheick Tiote drilled an effort wide after a flowing move.
But in the meantime, the visitors might have got themselves back into the game as Wilfried Zaha made his mark.
The winger, who had started on the right, decided to try his luck on the opposite flank and tricked his way past Debuchy before firing in a 29th-minute shot which Krul blocked instinctively with his trailing leg.
Zaha got in behind Debuchy once again two minutes later, but this time the defender recovered to make a vital interception.
Pardew's men restored a measure of order as the first half approached its conclusion, but the game was far from over as they reassembled in the dressing room with Newcastle old boy Craig Bellamy replacing Kim Bo-kyung at the break.
Bellamy made an impact as he gave the visitors greater impetus going forward, and his pass to Campbell allowed him to send in a right-wing cross which floated across goal and just wide of the far post.
Central defender Mike Williamson saw a 57th-minute shot deflected wide as Newcastle responded, but the flow of play was largely towards his goal, although with the Bluebirds unable to find any kind of cutting edge.
But they might have been back in the game with 14 minutes remaining when Jordon Mutch headed down for substitute Kenwyne Jones to poke the ball towards goal, only for Krul to block. And when the Dutchman spilled Bellamy's cross seconds later, Aron Gunnarsson's effort was cleared off the line by Coloccini.
But Cardiff's fate was sealed at the death as Remy tapped home after Tiote's 87th-minute shot had been blocked into his path, and Taylor completed the scoring in injury time when he stabbed home from Remy's knock-down.