Susan auditioned for the talent show, which is an all-star spin-off which sees former winners and finalists compete, and performed Wild Horses to the delight of the four judges. Judges Simon Cowell, Howie Mandel and Heidi Klum all applauded Boyle's performance, but it was Mel B who ultimately pressed the coveted "Golden Buzzer" on her behalf.
Boyle's cover of Wild Horses reached number nine in the United Kingdom singles chart in December 2009 - her highest entry.
Simon Cowell told Susan she was the "defining" contestant of the Got Talent series.
"What an absolute honour and pleasure it is to be sitting here and listening to you and your angelic voice", she said.
Boyle, 57, tweeted after the performance.
"I'm excited to show Simon how much I've grown since the last time he saw me".
Despite being the favourite to win the show back in 2009, Boyle lost out on the top spot to dance group "Diversity". "And I want to be the woman who gives you something you deserve".
"Susan, I'm genuinely beyond thrilled that you're here tonight", Cowell told Boyle.
America's Got Talent: The Champions, which premiered on Monday, 7th January 2019, brings back successful contestants from earlier versions of the United Kingdom and U.S. versions of the show. However, all the attention catapulted her into the spotlight, where she released her debut album I Dreamed a Dream.
Despite finishing second on Britian's Got Talent, Boyle says she already feels like a champion "for those who don't have the confidence to do things, for those who don't have a voice (and) the ones who people tend to ignore".
Another added: "Susan Boyle is back and she looks hotter than ever folks!"
Despite being a runner-up on the show, she went on to sell over 25 million records worldwide.