Simon, 54, praised the 19-year-old Londoner after he stormed to victory on Saturday night's final of the BBC One singing competition.
Taking to Twitter in the early hours of this morning (7 April), Simon tweeted: "Congratulations to Jermain the winner of the voice uk. You deserved it."
Jermain, who is a youth politician for the Labour Party, beat Sally Barker, Christina Marie and Jamie Johnson to win the third series of the talent show and land a record deal with Universal Music.
Simon wasn't the only person to send Jermain praise, as a string of celebrities congratulated him after his victory, including former Voice coach Danny O'Donoghue, last year's runner up Leah McFall and and Labour leader Ed Miliband.
Congratulations to Jermain the winner of the voice uk. You deserved it.— Simon Cowell (@SimonCowell) April 7, 2014
Jermain, who was coached by Black Eyed Peas star will.i.am on the show, even got a personal message from Cheryl Cole, as the former Girls Aloud star called will live on air to say that Jermain was "amazing".
During the series, Jermain revealed his ultimate ambition was to become "the first singing black prime minister".
Speaking on BBC Radio 5 Live on Sunday morning (April 6), Jermain said: "What's going to happen next is I'm going to record some music, release it and hopefully take over the world! I'm in for a bumpy ride, but I'm definitely going to work hard and make sure I can hold on and bear the ride."
The Voice UK has been a huge success this year with the arrival of new judges Kylie Minogue and Ricky Wilson joining original coaches will.i.am and Tom Jones.
Emma Willis and Marvin Humes also stepped in as the show's new presenters, replacing Holly Willoughby and Reggie Yates.
Elsewhere, Simon will be coming back to our screens with Cheryl on The X Factor later this year, as the pair make their return as judges on the popular ITV talent show.
Got an iPad or iPhone? Reveal Mag has been especially designed to fit!
Watch Jermain perform' And I Am Telling You' in the final below: