Benitez was employed in November after Roberto Di Matteo was sacked when Chelsea became the first holders to exit the Champions League at the group stage.
With Chelsea now on course to finish third or fourth in the Barclays Premier League, depending on the result in Sunday's match with Everton, the Spaniard has fulfilled his brief ahead of his departure at the end of the season.
And, following last night's 2-1 Europa League final defeat of Benfica which means Chelsea are the first team to hold both European titles simultaneously, Cahill praised the much-derided former Liverpool boss.
"Whatever's happened throughout the year with the manager, you have to give him credit," Cahill said.
"He ends this season with a better [Premier League] season than last year and we've just won a trophy. When you sit back and reflect on that he's done a great job."
Benitez allowed the players to bask in the glow of victory, Cahill said.
The former Bolton defender added: "He's humble like that. He's clearly thrilled that we've won the cup. He lets us enjoy it and that's what we're going to do."
Chelsea will play their 69th and final game of the season against Manchester United-bound David Moyes' Everton this weekend before embarking on the traditional lap of appreciation in front of their own fans at Stamford Bridge.
Due to his prior association with Liverpool and past duels with Jose Mourinho, who is expected to be confirmed as his successor this summer, Benitez has experienced numerous jeers since his November appointment and his reception could be mixed this weekend.
"Everyone's entitled to their opinion," Cahill said.
"I'm not sure whether it [the supporters' opinion] will change or not.
"Whether you sort of love him or hate him as a Chelsea fan, you have to step back and realise he's done a great job this season for us and we've finished strongly.
"As players we've worked hard towards the end of this season, played a lot of games, sometimes you get rewarded for hard work.
"The manager's kept his head down and worked hard and been rewarded as well.
"The most important thing at the end of all this is the club. At the minute we hold both trophies, it's something to be proud of."
Cahill was preparing for extra-time when his central defensive partner Branislav Ivanovic netted the stoppage-time winner as Chelsea won a trophy at the eighth and final attempt this term.
Cahill added: "I don't think we thought about losing. We had to win.
"It was the last chance to win something. I think we did save the best until last.
"We've got character in the dressing room and the big players turned up at the right time for us."