Kevin Gameiro and Rodrigo Moreno struck first-half goals to give Marcelino's dominant Valencia control of the final in Seville's sweltering Benito Villamarin stadium.
Record 30-times Cup winners Barcelona struggled without injured forwards Luis Suarez and Ousmane Dembele but Lionel Messi pulled the Catalans back into the game with a close-range finish.
Goncalo Guedes missed a gilt-edged chance in stoppage-time for Valencia but they held on to win their first major trophy since last lifting the Cup in 2008.
"I'm so happy because for me, my family, it's incredible," said Valencia captain Dani Parejo. "A club like Valencia deserves a lot more joy like this. I don't have the words, it's incredible.
"We've made history in a really significant year, our centenary year."
Valencia finished fourth in La Liga after a strong second half of the season, reaching the Europa League semi-finals and ending an impressive campaign with this victory.
By contrast, Barcelona's campaign collapsed in the last fortnight as they threw away a three-goal Champions League semi-final lead to be eliminated by Liverpool before letting the Cup slip out of their hands.
Barcelona were bidding to lift themselves from their humiliation on Merseyside by securing the ninth domestic double in their history, but despite Messi's efforts they were over-run by a determined and well-drilled Valencia side.
Gerard Pique was forced to clear Rodrigo's effort off the line before Gameiro blasted Marcelino's side ahead in the 22nd minute after good work from Jose Luis Gaya.
The Catalans failed to create openings and Rodrigo nodded home the second after Carlos Soler whipped a ball across the face of goal.
Messi struck the post with a delightful outside-of-the-boot effort before slotting home the rebound when Jaume Domenech saved Clement Lenglet's header for his 51st goal of the season, but it was not enough.
"Valencia are worthy champions and it's also been a good year for us," said Pique.
"It's always a good year when you win La Liga but the expectation was to have an even better year and that's not been the case. The season ends with a bittersweet feeling, because it could have been better.
"We aren't worrying about the manager's future, we must analyse ourselves and try to improve. The other decisions aren't in our hands, but we've said more than once that we would like him to stay on."
(Reporting by Rik Sharma, editing by Ed Osmond)
Share
