After the announcement was made by host Marvin Humes, Jermain was seen putting his head in his hands in disbelief. The 19-year-old Londoner looked stunned to have won the BBC talent show, making it the first time a male contestant has won the singing competition.
Standing alongside his coach will.i.am, Jermain paid tribute to the American rapper and thanked his fans for their support.
Jermain the winner with hosts Emma Willis and Marvin Humes
"I want to thank Will for everything he's done for me over the past few months," said Jermain. "He's been the best coach ever. I want to thank God for providing me with this opportunity and all the opportunities I've had."
"I want to thank my family and friends, because this is not just an achievement for me, but an achievement for everyone in the UK who has had a dream and worked hard to achieve that dream," he added. "I want them to know that if you work hard for your dream you will achieve it."
Mentor will.i.am and Jermain
After the live show Jermain took to Twitter to send out more inspiring messages. "Work hard for your dream & you can achieve it. So humbled & blessed to have shared the stage with all the artists this year. Thank you all," he wrote, before adding, "Overwhelmed & Emosh!!!"
Supporters and those that had worked with Jermain on the show were quick to congratulate the rising star, with Marvin tweeting a photo of the pair backstage. "Here is your winner! @JermainJackman congrats bro... the world is your oyster! #thevoiceukFINAL," he posted.
"Sneaky willy for the win, congrats brother @iamwill, good on ye @JermainJackman, you deserve it," tweeted The Script frontman and former show mentor Danny O'Donoghue.
Labour party leader Ed Miliband and Jermain
Jermain, who is a young Labour Party activist and has said he aims to become the first black prime minister in the UK, had previously met Labour leader Ed Miliband at a radio studio.
The politician looked thrilled to see Jermain win, calling him "such a decent guy" and tweeting, "Huge congratulations to @JermainJackman. Knew you were an incredibly special singer from the first time I heard you. #TheVoiceUK."
Jermain sang And I'm Telling You in the final live show
For his final performance Jermain chose to sing And I'm Telling You by Jennifer Hudson, which he had sung at his first audition. Coach will.i.am showed his enthusiasm by dancing on his chair and applauding from the start.
The pair had originally met at a music festival, when the Black Eyed Peas singer encouraged Jermain to apply for the next series of The Voice.
Jermain beat fellow contestants Sally Barker, Christina Marie and Jamie Johnson to the final.