Leyland told the Tigers after the end of the ALCS that he would retire, according to Rosenthal. Detroit lost the series 4-2 to the Boston Red Sox.
The 68-year-old had signed one-year contract extensions each of the past two seasons. His retirement comes as a bit of a shock; both Chris Iott off MLive and Tom Gage of the Detroit News expected him to return on another one-year deal.
Leyland has been the Tigers manager since 2006, compiling a 700-597 record with Detroit over the past eight seasons. The Tigers won two AL Pennants under Leyland, and have earned three consecutive AL Central titles.