When Fox News anchor Megyn Kelly moves to prime time this month, replacing Sean Hannity in the coveted 9 p.m. slot, the lawyer-turned-anchorwoman is expected to draw an even larger audience to a network that’s already handily beating the competition.

Until she went on maternity leave following the birth of her third child in July, Kelly anchored the afternoon news show “America Live.” Now, Fox is betting that moving its rising star to prime time will help the network win back viewers between 24 and 52 that advertisers covet and Fox has been losing.

Fox News ranked No. 1 in overall viewership for 140 straight months, with an audience bigger than MSNBC, CNN and CNN Headline News combined. But Hannity’s audience among 24-to-52 year olds dwindled by 26 percent over the past year while prime-time talker Bill O’Reilly’s share of those viewers dropped 25 percent, according to Nielson ratings.

The appeal of Kelly’s show, insiders say, will be the way her smart, direct approach contrasts with the wonky style of struggling MSNBC anchors Chris Hayes and Rachel Maddow.

“The genius of her, and what will be the genius of her show, is that she will be smart enough to ask the good questions but not so vain that she doesn’t ask the right ones. She’s never afraid to say, ‘Back up, slow down, what does that mean?’ That’s how you get the good answers,” one Fox executive told the Washington Examiner.

Kelly, 42, practiced law for nine unsatisfying years at the global firm Jones Day before landing a reporting job at WJLA-TV in Washington in 2003. The next year, she was working for Fox, covering Supreme Court nominees and other issues, before taking over “America Live” in 2007.

“Megyn is an exceptional talent who has successfully filled and surpassed each role we have given her at the network,” Fox CEO Roger Ailes said in a statement. “Her ability to command the screen, delve into the facts and lead a debate is what makes her one of the most sought-after anchors in the business.”

Kelly earned her reporting chops doing hard news, including the 2006 Duke University rape case, when she broke news that helped vindicate three wrongly accused lacrosse players.

In an era of the loud and shrill, Kelly is confident, calm and no-nonsense on air. When RedState Editor Erick Erickson and Fox Business Network’s Lou Dobbs claimed on her show in May that working mothers are bad for the country, Kelly, whose other children are 3-1/2 and 2 years old, immediately challenged them, forcing them to back down without ever raising her voice.

Hannity, who just re-upped with Fox, is stoic about Kelly replacing him.

“Let’s just say in the end I’m very happy,” he told his radio audience in August. “That’s all I can say at this point.”

A Fox News spokeswoman called the Washington Examiner to say that the date of Kelly's move to prime time has not been officially confirmed.