Pierzynski, 35, must pass a physical examination on Friday before the deal becomes official.
He has played the last eight years with the Chicago White Sox, who with Pierzynski catching won the 2005 World Series. Pierzynski has also played for Minnesota and San Francisco.
He has a career batting average of .284 with 155 home runs and 730 RBI. He hit a career-best 27 home runs last season with a .278 average.