Vunipola, 31, appeared in court on Sunday following the episode at a bar in the island's capital Palma in which police reportedly tasered him.
The court said in a statement that Vunipola had caused injury to a police officer who was attempting to subdue him. He was ordered to pay 500 euros ($535) in compensation to the victim as well as a fine of 240 euros.
The court said Vunipola had been convicted of "one count of assault and a minor count of (causing) injury".
English Premiership club Saracens said they would deal with the matter internally.
Vunipola released a statement on X, formerly Twitter, saying: "I can confirm I was involved in an unfortunate misunderstanding when I was leaving a club in Mallorca on Sunday, which got out of hand."
He insisted there was "no violence, no fight and I did not threaten anybody at any stage, with bottles or chairs or anything else".
"The Spanish police investigation is now closed, and I am flying back to the UK today," Vunipola added, saying he "unreservedly apologises" to those involved.
The Mallorca-based Ultima Hora newspaper said Vunipola was tasered twice by police in the incident and it took eight police officers to subdue and handcuff him.
The newspaper's website carried a video showing a handcuffed Vunipola, as well as other men, being led from a police van into a courtroom.
"We will of course deal with this incident internally, and will not make any further comment until then," said Saracens in a statement on social media.
Vunipola is expected to leave Saracens at the end of this season and has been linked with a move to French club Montpellier.
He has won 75 England caps, making his Test debut against Argentina in 2013. He is not currently part of the England squad.
Vunipola made an appearance as a second-half substitute for Saracens in their 15-12 victory over Bath on Friday.
The club are not scheduled to play again until May 11.
Saracens are second in the English Premiership and are chasing a sixth league title in the last 10 seasons with two rounds of regular season games left before the play-offs.
