The NBA London game, hosted by AEG, features the Atlantic Division rivals that struck a trade for the top overall pick this year. Boston sent the No. 1 pick to Philadelphia, which drafted Fultz, in exchange for the third overall pick in June's draft and either a first-rounder in 2018 or 2019.
Boston selected Jayson Tatum with the third pick.
The Celtics, who added free agent Gordon Hayward to a lineup featuring Isaiah Thomas and Al Horford, hope to improve on last season's campaign, when they reached the Eastern Conference finals after posting the East's best regular-season record (53-29).
"I look forward to coming back to London with the Sixers after visiting for the first time this summer," Embiid said in a statement. "We are a young, hungry team, and we will be sure to give the fans an exciting game against Boston in January."
This will be the NBA's eighth regular-season game in London, and it is the second appearance for Boston and Philadelphia, which have played preseason games in London and Manchester, respectively.
"This will be our 16th game [overall] in London where our events have become an annual opportunity for basketball fans across Europe to come together and share their passion for the NBA," commissioner Adam Silver said.