The Newcastle United legend says the Spaniard's decision is "brilliant" for the club but suggests he did not expect things to work out this way.
Benitez signed a new three-year deal at St. James' Park on Wednesday and will manage in the English second tier for the first time next season, just half a year after coaching one of Europe's biggest clubs in Real Madrid.
Ex-Magpies midfielder Nolberto Solano hailed the club's achievement in persuading the Spaniard to stay as their biggest moment since the appointment of Sir Bobby Robson in 1999
Shearer shares his former teammate's enthusiasm for the decision, but admits that he was surprised that the 56-year-old was prepared to stick with the club.
"It's a tough league, the Championship and hopefully he can get Newcastle back into the Premier League within one season, at the first attempt.
"The fans wanted him to stay and he's done that. I'm a little surprised, I have to say, but it's brilliant for Newcastle."
Benitez oversaw a remarkable late revival in the final weeks of the campaign, leading the club to a six-match unbeaten run to finish the season, but it was not enough to save the doomed North East club.
However, his new deal will give optimism for Magpies fans that next season might hold promise after such a disillusioning year.