The Backstreet Boys singer will open for Spears during several dates on the South American leg of her tour beginning November 20 in La Plata, Argentina, according to Dorough's official website.
Dorough's stint will include shows in Chile, Peru, Colombia and Venezuela.
"I'm so excited that I'm going joining @britneyspears on several dates of the 'Femme Fatale' tour!" he wrote on his Twitter page on Monday.
The Backstreet Boys told Digital Spy this week that they have begun work on a new album, though the band have no release date in mind.
"It's too early to say what the direction of the record will be - right now we're just writing and gathering songs. Our last album was a bit more Euro-dance but we're considering moving back to our pop-rock sound," Dorough said.
Dorough will release his first solo album Back To Me on November 15.
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Watch the video for Howie Dorough's '100' below: