The Spaniard has gone from from the top of La Liga with Real Madrid to the foot of the English Premier League in little over two months.
After six days of speculation, the club sacked former England coach Steve McClaren Friday following a desperate run of results that has left it second from bottom of the table.
Now it has turned to the 55-year-old, a former coach of Inter Milan, Valencia and Chelsea, who won the European Champions League with Liverpool.
"I have the pleasure to confirm I have committed to a legendary English club, with the massive challenge of remaining part of the Premier League," Benitez said in a statement on the club's website
"It will be a challenge not just for me and my staff but for the players, the club and the fans.
"All of us must push together in the same direction and with the same target in mind. This is the reason why I'm going to ask for your total support to successfully complete this task.
"Personally, it means my return to the Premier League, closer to my home and my family. I can't be happier. C'mon Toon Army! The club and I need your total involvement!"
Newcastle confirmed Benitez as its new manager, and three new backroom staff, on a three-year deal. He took over at Real Madrid in June last year but was sacked in early January.
The news came just hours after McClaren was relieved of his duties. The 54-year-old has overseen a disappointing campaign in which Newcastle has won just six matches all season.
It sits one point from safety and in danger of missing out on a share of a bumper Premier League television deal that kicks in next season.
Crucially, Benitez has been appointed manager, not head coach as McClaren was, which indicates he will have more of a say in the running of the club and especially transfers.
Newcastle's managing director Lee Charnley said: "In Rafa we have, without doubt, secured the services of one of Europe's top managers.
"He has managed some of the most successful teams at the very highest level of the game and we are proud to now have him as our manager.
"Our sole focus now is to give our full support to Rafa, his coaching team and the players in order to secure our status in the Premier League."
After retiring as a player, Benitez spent nearly a decade coaching in Real Madrid's youth setup and had spells with Real Valladolid, Osasuna and Extremadura before joining Valencia.
He led the club to its first La Liga title in 31 years in 2001-02 before repeating the feat, plus a UEFA Cup crown, in 2003-04.
Benitez spent six seasons in England with Liverpool, the highlight being a remarkable Champions League win against AC Milan in 2005 -- when the Reds came back from 3-0 down in the final to triumph after a penalty shootout.
A less successful spell in Italy with Inter followed before a six-month stint as interim manager at Chelsea after Roberto Di Matteo was sacked, winning the second-tier Europa League. He then spent two seasons back in Italy with Napoli, winning the domestic cup competition in 2014.
Real Madrid came calling after sacking popular Champions League winner Carlo Ancelotti, but Benitez lasted barely six months -- his popularity plummeted after a 4-0 crushing at home to arch rival Barcelona in November.
Now he has 10 games to save Newcastle's season before he can think about building any sort of legacy at the club -- which saw little return on its heavy spending in the transfer market under McClaren.