Posnanski began his journalism career as a multi-use reporter and an editor at "The Charlotte Observer". He also worked as columnist at "The Cincinnati Post" and "The Augusta Chronicle" before taking a columnist job at "The Kansas City Star". Posnanski worked at the Star full-time from October 1996 to August, 2009. He was a Senior Writer for "Sports Illustrated" until April 2012, when he announced that he would work for Sports on Earth, a new internet joint venture between "USA Today" and Major League Baseball Advanced Media. His first column for Sports on Earth was published online on August 26, 2012. In February 2013, he became the national columnist for NBC Sports. In February 2017, he became a national columnist for MLB.com and contributor on the MLB Network.