Overbay, an 11-year veteran with 130 career homers in 1,241 games, was designated for assignment after batting .227 with eight homers, 37 RBI and a .300 on-base percentage in 103 games for the Pirates this season.
The 34-year-old left-handed batter, who signed a one-year contract with Pittsburgh in the off-season, last year socked 20 homers with 67 RBI in 154 games with the Toronto Blue Jays.
The Pirates obtained Lee, 35, also a left-handed-hitting first baseman, for minor leaguer Aaron Baker in a Saturday trade with the Baltimore Orioles.
Pittsburgh also announced it had optioned infielder Pedro Ciriaco to Class AAA Indianapolis to make room for another player acquired at the trade deadline, outfielder Ryan Ludwick.
Swim Week Miami Beach 2014 [PHOTOS]