The deal came only minutes after the San Francisco's NL West rival, the Los Angeles Dodgers, acquired outfielder Shane Victorino from the Phillies.
Pence, who has 17 homers and 15 doubles this season, will likely start in right field for the Giants, who are tied with the Dodgers for first in the division, 3 1/2 games ahead of Arizona.
Pence, 29, is eligible for arbitration in the off-season after making around $10 million this season. He has clubbed 131 homers and 172 doubles over 835 career games -- 680 of them with Houston.
Schierholtz, who has spent his entire six-year career with the Giants, has a .257 batting average with five homers in 77 games this year. The outfielder sports a .270 average with 23 homers in 503 career games.
Also going to Philadelphia were catching prospect Tommy Joseph, minor league pitcher Seth Rosin and cash.