Stewart, who was convicted of multiple felony charges in 2004, was prosecuted by former FBI Director James Comey, and served five months in federal prison on charges related to a 2001 stock sale.
Comey was fired by Trump last year and has since become an outspoken critic of his administration.
Trump has shared mixed opinions about Stewart in the past.
In a 2006 letter to Stewart, the president blamed her for the poor ratings of NBC's "The Apprentice: Martha Stewart," a spinoff of Trump's "The Celebrity Apprentice."
The next month, he said of Stewart: "She's a wonderful woman."
Years later, in a 2013 tweet, Trump wrote: "She looks terrific, better than ever, any guy would be lucky to be with her."
Patrick Fitzgerald, a personal friend of James Comey, oversaw the prosecution of Blagojevich on public corruption charges in 2011. Fitzgerald joined Comey's legal team following the former FBI director's firing last year.
Blagojevich is in the sixth year of a 14-year sentence in Colorado prison. The Illinois Democrat was found guilty of attempting to trade the U.S. Senate seat vacated by Barack Obama for money or favors.
"I am seriously thinking about – not pardoning – but I am seriously thinking of a curtailment of Blagojevich," the president said Thursday, before a reporter offered the word "commutation."
In a statement, the former governor's wife, Patti Blagojevich, said the president's comments were encouraging.
"[Trump has] given us something that has been hard to come by recently…hope," she said. "From the beginning, we've eagerly awaited the day when Rod could come back home where he belongs, and we continue to pray our family will be made whole again soon."
Blagojevich also has a connection to Trump's "The Celebrity Apprentice," appearing on she show in Spring 2010. Trump noted that Blagojevich was on the show "for a short time" in his remarks about the potential commutation.
Representatives for Stewart did not immediately respond to requests for comment.