The Britain's Got Talent runners-up are said to have agreed a deal with the Syco label, and have already started recording their debut LP.
Cowell has said that the album will be released on September 3, The Sun reports.
"Simon knows that to make money from them he needs to move fast," a source said. "Get the first album out as soon as possible before people have moved on.
"September is also a good time as The X Factor will be in its live stages, so there is a chance to get them on the show and plug the album."
Cowell said: "This show is designed to give people like Jonathan and Charlotte an opportunity. Their debut album is going to be stunning."
The album will be a collection of new tracks and cover versions, including their version of 'The Prayer', which they sang on the live final.
Jonathan & Charlotte will be working with Graham Stack, who produced the first three G4 records, on their album.
Jonathan Antoine said: "I'm still pinching myself that we are actually making our own CD," while Charlotte Jaconelli added: "This is a dream come true for us."
Cowell was rumoured to be offering the pair a £1 million recording contract regardless of their Britain's Got Talent result.