Fender and Dean's Rein Me In won Song of the Year at Saturday's ceremony in Manchester for the duet - which originally appeared on Fender's album People Watching before the pair reworked the track.
It marks the first-ever BRIT win for Dean - who is up for five prizes at the ceremony - whilst Fender takes home his fourth prize overall.
"I think this is a beautiful song and it's been a pleasure to be a part of it," Dean said after accepting the prize from Robbie Williams.
Fender said he wrote the song "about four years ago and I loved it then".
"Olivia has made it her own, so I want to say thank you to Olivia and thank you to the fans."
The triumph continues the awards success for Dean, who declared how she was the "product of bravery" after triumphing in the Best New Artist category at the Grammys earlier this month.
The Man I Need hitmaker - who also performed that track at the BRITs - said at the time: "I never really imagined that I would be up here, let alone nominated. So thank you so much.
Rock band Wolf Alice won group of the year.
In her acceptance speech, singer Ellie Rowsell thanked "all the pubs, clubs and grassroots venues across the country where we quite literally learned to play our instruments and write our songs".
Organisers already announced several winners ahead of Saturday's ceremony, with Noel Gallagher named songwriter of the year and PinkPantheress crowned producer of the year. At 24, she is the youngest ever and the first woman recipient of the prize.
Ozzy Osbourne, the late frontman of the heavy metal band Black Sabbath, will be honoured with a lifetime achievement award "in recognition and celebration of his inimitable impact and influence on music worldwide", organisers said.
Known to fans as "The Prince of Darkness", Osbourne died in July aged 76, around two weeks after Black Sabbath's emotional farewell gig.
This year's BRITs are being held in the northern English city of Manchester, the first time the awards ceremony is being held outside of London.
with Reuters
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