Zidane took over from Rafael Benitez in January, leading Madrid into second in La Liga and into the European decider against Atletico on Saturday.
Karembeu, who was at the club from 1997-2000, said his fellow Frenchman had already proven to be a success at the helm.
"'Zizou' took the team at a moment where it was the best solution for the club," the 45-year-old said.
"Zidane found the way to win, to get good results and to come up in the Spanish league. And in the same time, he brought Real Madrid to the Champions League final, so it’s a great achievement.
"It means a lot of work, a lot of sacrifices in order to bring the team at the top and to come back on Barcelona.
"Now, I just hope they'll be rewarded in the final. And everybody knows that when Real Madrid plays a final just one thing is important - the win."
Real and Atletico are meeting in the Champions League final for the second time in three years.
Madrid clinched their elusive 10th crown when the teams met in 2014, winning 4-1 after extra time in Lisbon.
Karembeu hopes the big-game experience can be a factor for Madrid.
"Real know how to deal with emotions and pressure. They have their history in finals. Hopefully, being a Real Madrid fan, they can do it," he said.
"Also for the fact it will be Zizou's first final as a manager… But still, Diego Simeone will be there. They are in good form, they want to win. His seasons are always successful.
"They also deserve the title but Real, once in a final, they will give everything they have to win it."