Zimmerman was recalled from his rehabilitation assignment in the minors and was in the starting lineup against St. Louis.
"It feels great," Zimmerman said. "Throwing, running, hitting, everything feels fine. I wouldn't be up here if I didn't think I could play the way I'm supposed to play."
The Nationals optioned right-handed pitcher Craig Stammen to Triple-A Syracuse.
Zimmerman hit .357 with one home run and four RBIs in eight games before being sidelined. He had been on the disabled list since April 10 and had surgery on May 3 to repair a tear on his left side.
"It's great to have him back," Nationals manager Jim Riggleman said. "Ryan is so much a part of the past here, the future here, and we need him here now. He's just such a good ballplayer."
The Nationals hope Zimmerman's return can help jump-start an offense which has struggled so far this year. Washington's team average of .229 is last in the National League, and the Nationals have scored three runs or less in eight of their last 10 games.
"Me coming back is not going to make us score 10 runs a game," Zimmerman said. "I wish, I hope, we do, but it takes a team. My goal is just to be positive, come up here, have the same energy I always have."
Zimmerman was 8 for 21 with three RBIs in six games during his rehab assignment. Although he said he has some lingering soreness, and expects it will continue until he can fully heal in the offseason, he is ready to get back on the field for the Nationals.
"It's been a long, frustrating two months," Zimmerman said.