The 25-year-old spent most of last season in Triple-A with the Iowa Cubs. He was 8-3 with a 3.63 ERA in 28 games, including 15 Minor League starts, and was designated for assignment by Chicago in late September.
A former seventh-round Draft pick, Atkins has a career 5.25 Major League ERA, making seven relief appearances for Chicago over the past two seasons. This season, he was 0-0 with a 6.30 ERA in five appearances out of Chicago's bullpen. In 10 innings of work, Atkins struck out 10 batters.
The signing, which is expected to be the first of many low-risk invites, was first reported on the Baltimore Sun's website on Monday afternoon.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.