The stand-up told USA Today that the series is the perfect fit for him because of its tongue-in-cheek tone.
"That's the best fit for me for the first time around," he said. "Readers in that world are more familiar with me as a comedian so I think if I started writing a really serious book - like if I just took over Thor or something - people would be like, 'Uh, what's that guy doing?'
"But Deadpool, people are like, 'Oh yeah!' Readers who have no idea what we're going to do think it's a good fit."
Posehn will pen the Marvel NOW! series with Gerry Duggan, with artist Tony Moore handling interior illustrations. The first arc sees the 'Merc with a Mouth' taking on an army of undead presidents.
Deadpool #1 arrives in stores tomorrow (November 7).