Harper was activated off the injured list and was in the lineup, batting third at designated hitter when the Phillies took on the Los Angeles Dodgers in the middle game of a three-game series.
Harper went 0-for-4 and struck out three times in the Phillies' 13-1 loss.
The return for the two-time NL MVP came 160 days after Harper had Tommy John surgery on his right elbow, the fastest return on record by a major league player from that surgery. It occurred at the ballpark where he made his major league debut in 2012.
"Medically it is surprising, but by Harper genetic standards probably not," Harper's agent, Scott Boras, said while the Phillies were taking batting practice. "I remember last Thanksgiving we were talking about when he could come back and he mentioned May and I told him not to tell anyone that."
When Harper had surgery on Nov. 23, the Phillies said he was expected to return around the All-Star break in mid-July. He was cleared to play after an appointment with Dr. Neal ElAttrache on Monday morning.
"I tried to go through the whole process and understand where my body and mind was. I tried to do everything I could to get to this point. It's been a grind," Harper said before Monday's game.
Harper -- who entered with a .292 batting average and six homers in 26 games at Dodger Stadium -- said he will continue to wear a brace on his right elbow while hitting. He wore it most of last season after originally suffering the injury last April and batted .286 with 18 homers and 65 RBIs.
The 30-year-old Harper first suffered a small ulnar collateral ligament tear in his elbow in April. He had a platelet-rich plasma injection in May and shifted to the DH role.
When it comes to the possibility of another injury or if he is coming back too soon, Harper said he is healed the way he needs to be to play.
"Whenever you have a major surgery something could happen. It wouldn't matter from right now to two months, we're healed to where I need to be and play the game smart and the right way," Harper said. "I'm not going to push the craziness of how I play and understand I help my team when I am on the field and not off it."
Harper's return also comes at a great time for the Phillies. The defending NL champs are now 15-16, but have won seven of their last 11 games.
It adds more power to a deep Philadelphia lineup. The Phillies went into Tuesday's game third in the majors with a .271 batting average. They have been generating their share of hits with soft contact as Statcast's expected batting average is .244.
Philadelphia added Trea Turner-- a former teammate of Harper's in Washington -- to join a batting order that includes Kyle Schwarber, Nick Castellanos and J.T. Realmuto. Brandon Marsh, who was acquired at the trade deadline from the Los Angeles Angels last year, is fifth in the majors with a .337 batting average.
"It really creates a long lineup," manager Rob Thomson said. "When you see it, you're going to see a couple pretty good hitters way down there because Harper is back. Once he gets hot, we're going to be a handful."
Thomson moved Schwarber from fifth back to leadoff, where he batted most of last season. Turner is hitting second followed by Harper, Castellanos and Bryson Stott.
Thomson said with the number of days off that the Phillies have in May, the expectation is that Harper can be in the lineup every day as long as he remains healthy.
When it comes to the possibility of when Harper will return to the field, Thomson said that is likely to be a couple months away. Harper has played mostly right field, but is taking grounders and throwing from first base.
Thomson's biggest worry at the moment is making sure Harper gets off to a good start at the plate.
"I wouldn't be surprised where it is going to take some time to get true timing back but I'm pretty confident in his abilities," Thomson said.
To make room for Harper, the Phillies optioned outfielder Jake Cave to Triple-A Lehigh Valley.
ESPN Stats & Information and The Associated Press contributed to this report.