The 62-year-old Scottish singer - who rose to fame after coming second to Diversity on the ITV talent show in 2009 - performed during the 2023 final with the cast of Les Miserables from London's West End.
Boyle confessed she had feared she might never perform again.
Asked by hosts Ant McPartlin and Declan Donnelly how it felt to be back on Britain's Got Talent after 14 years Boyle said: "It feels great. It's really good."
She added: "It's extra special for me actually, last April there, I suffered a minor stroke and I fought like crazy to be back on stage and I have done it."
Head judge Simon Cowell: "It's so good to see you Susan. I knew you weren't well but if anyone was going to come back it was you."
Boyle sang I Dreamed A Dream from the French revolution musical, the same song she performed in her very first audition for the show.
Norwegian comedian Viggo Venn - who wears hi-vis vests as part of his act - was voted the winner of this year's series by the British public.
He joked: "I feel extremely visible right now, thank you so much."
When Ant and Dec said he had captured the hearts of the public he said: "Not just the heart of Britain but the heart of Simon [Cowell]. Thank you so much everyone who voted for me."
— BGT (@BGT) June 4, 2023
Magician Cillian O'Connor, 14, and dancer Liliana Clifton, 13, were named the two runners-up of this series.
During his act Venn used the "s***" word as he pretended something had gone wrong.
Ant McPartlin said afterwards: "We must apologise for any bad language that you might have heard during that. Not naming names. Somebody did."
Watch: Susan Boyle voted one of BGT's best acts of all time