Final answer:
Susan Boyle became famous on 'Britain's Got Talent' 2009 by singing 'I Dreamed a Dream' from 'Les Miserables', which is a notable 1980s megamusical.
Step-by-step explanation:
Susan Boyle made a significant impact on 'Britain's Got Talent' in 2009 by performing the Broadway classic 'I Dreamed a Dream' from the musical 'Les Miserables'. Les Miserables is one of the notable megamusicals of the 1980s, a trend that featured blockbuster productions with large commercial profits.
This song choice highlighted her powerful voice, connecting with audiences and catapulting her into an overnight sensation.