The SoftBank Hawks announced the signing on their website.
Penny, 33, spent 2011 with the Detroit Tigers, his sixth team in the big leagues. The right-hander went 11-11 for the Tigers.
Penny is a two-time All-Star (2006-07) whose best seasons came in Los Angeles with the Dodgers. Penny went 16-4 with a 3.03 ERA in 2007, finishing third in the Cy Young Award voting, after leading the National League in wins with 16 in 2006.
Penny came up with the Florida Marlins in 2000 and has a career record of 119-99.