A rather large move in the world of digital journalism: Tim O’Brien is leaving his post as the executive editor of the Huffington Post, a spot from which he has overseen “all of the site’s original reporting efforts.”

Here’s the note from Huffington Post name partner Arianna Huffington:

After two years overseeing our national reporting staff in New York, Tim O’Brien is leaving to work on the second installment of his five-book publishing deal. I’m truly grateful to him for helping us build such a robust and well-oiled original reporting infrastructure, including a crack team of news editors and copy editors, for helping launch the Huffington. magazine, and for editing David Wood’s series that won HuffPost a Pulitzer. In the next few days, Tim’s reporters will transition to the editorial team of Howard Fineman, Peter Goodman, Ryan Grim, Kate Palmer, John Montorio, Sam Stein, and Amanda Terkel. We’ll miss him and look forward to his visits anytime he needs a break from the setting of his next historical novel.