After an 80–82 record the previous season which included a late-season collapse, the Phillies made several transactions in the 2018–19 offseason in order to improve the team.

On December 3, 2018, the Phillies acquired Jean Segura, Juan Nicasio, and James Pazos from the Seattle Mariners for Carlos Santana and J. P. Crawford.

Relief pitcher David Robertson signed a two-year deal with the Phillies on January 3, 2019.

On February 7, the Phillies acquired catcher J. T. Realmuto from the Miami Marlins for Sixto Sanchez, Jorge Alfaro, Will Stewart and international bonus slot money.

Finally, on March 2, the Phillies signed outfielder Bryce Harper to a record-breaking 13-year deal worth $330 million.