Financial terms were not revealed, but Johnson made $2.9 million with the Baltimore Orioles in 2003.
The 6-6 righthander rebounded from a rough 2002 campaign and matched his career high in wins last season, going 10-10 with a 4.18 ERA in 189 2/3 innings. He had a pair of stints on the disabled list in 2002, when he was 5-14 with a 4.59 ERA.
"Jason Johnson is a veteran starter we were looking to sign this winter," Tigers president Dave Dombrowski said. "He is a pitcher that will give us a lot of quality innings. He has a great deal of ability and upside potential that we feel can be realized. We are happy to have him on board and look for him to be one of the anchors of our rotation."
The 30-year-old Johnson joins a staff that includes Jeremy Bonderman, Mike Maroth and Nate Cornejo -- none of whom are older than 26.
Detroit had a severely inexperienced team and set an American League record with 119 losses in 2003. The Tigers signed second baseman Fernando Vina, outfielder Rondell White and catcher Mike DiFelice earlier this month.