The 39-year-old singer will be joined by Simon Cowell, Cheryl Cole and Louis Walsh on the hit show's judging panel, reported Daily Star.
"Mel has been in talks to join the show for months. There have been a few hiccups along the way to do with money and other commitments, but it's finally a done deal," a source said.
'Britain's Got Talent' judge Alesha Dixon, 35, has been battling Mel B for the coveted last spot on the TV singing contest. But she had no hard feelings and backed her to be a great judge.