The 31-year-old was bothered by a sore back while hitting .273 with four home runs and 40 RBIs in 111 games with the Braves and Mets last season. He also has had multiple concussions.
The Pirates expect Church to go into the season as their fourth outfielder. He also provides depth in case their top outfield prospect, Jose Tabata, does not reach the majors this season.
A left-handed hitter, Church batted .272 with 15 home runs, 43 doubles and 70 RBIs in 144 games with Washington in 2007. He was traded to the Mets after that season in a deal involving Lastings Milledge, now the Pirates' starting left fielder.
Atlanta did not tender a contract to Church because, by going to arbitration, he likely would have received a raise from the $2.8 million he made last season.
Church's deal includes bonuses of $75,000 each for 350, 375 and 400 plate appearances, $125,000 each for 425, 450 and 475 plate appearances and $180,000 each for 500, 550, 575 and 600 plate appearances.