Cox, 33, will coordinate Time.com's political coverage and write features and essays for print and Web versions of the magazine owned by the world's largest media conglomerate, Time Warner.
Her appointment is effective July 31, Time said Thursday. Cox, who also wrote the satirical Washington, D.C.-based novel "Dog Days," joined Time in March as a contributing writer.
"You can only write three-sentence posts for so long before you start to crave the comparatively literary world of newsmagazines," she wrote in an e-mail message.
Cox posted sarcastic and frequently foul-mouthed gossip and political commentary on Washington's elite and their underlings on the Internet under the pseudonym "Wonkette," from 2004 until earlier this year.
"I thought it'd be nice to work somewhere where my mom would not be embarrassed to tell her bridge club about," she wrote of her move to a prominent role in mainstream media.
"Of course, they all think the Internet is a ," she said, referring to 82-year-old Alaska Republican Sen. Ted Stevens' description of the Internet last month, comments since lampooned by bloggers and comedians.
Wonkette, owned by Gawker Media, became essential reading for many Washingtonians, particularly during the 2004 presidential election.
Cox built a reputation for beating established gossip columnists to the punch with juicy tidbits about politicians' peccadilloes and sightings of U.S. President George W. Bush's daughters in area bars.