Isaac agreed to a four-year, $80 million deal, his agent, Jeff Wechsler, told ESPN's Adrian Wojnarowski. Fultz agreed to a three-year, $50 million extension, according to his agent, Raymond Brothers of Roc Nation Sports.
"We are thrilled to keep both Markelle [Fultz] and Jonathan [Isaac] in a Magic uniform," president of basketball operations Jeff Weltman said in a statement. "They both have a very bright future and they mean a lot to our organization, both on and off the court."
Isaac, 23, is coming off a torn ACL in his left knee suffered in August during the NBA's restart in Orlando, Florida. The injury, which occurred shortly after his return from a hyperextension in the same knee, prematurely ended a breakout season for Isaac.
The 6-foot-11 big man posted career highs across the board last season. He joined Anthony Davis and Dwight Howard as the only players to average two blocks and 1.5 steals per game in a single season this decade and did so playing just 28.8 minutes per game.
To go along with his defensive prowess, Isaac averaged 11.9 points and shot 34% on 2.8 3s per game.
Fultz, 22, revived his NBA career with the Magic, who acquired him in a February 2019 trade with the Philadelphia 76ers.
A perplexing nerve condition in his neck and shoulder led to Fultz playing only 33 games across two seasons with the Sixers, but the point guard has been much more durable in Orlando.
In 72 games for the Magic last season, he averaged 12.1 points and 5.1 assists.