Talent show mogul SiCo consulted Twitter about the girlband's future earlier this week.
And the reaction must have been positive, because he confirmed that he had offered Fifth Harmony a contract yesterday (17 January).
Talking to People magazine, Simon said: "I knew from the girls' first performance at the judges' homes that we'd done the right thing.
"The chemistry between the girls both on stage and off is fantastic, and they are incredibly talented."
Fifth Harmony member Camila Cabello expressed her excitement over the deal, saying in a statement: "The fact that we're being given the opportunity to make music that we want feels like a dream we never want to wake up from.
"I literally have to pinch myself."
The band - who reached the final of last year's The X Factor USA - are rumoured to be working with producer Julian Bunetta on their debut album.
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