Mattis took the stage at the annual dinner -- an opportunity to crack jokes about local and national politics -- with an introduction from comic legend Martin Short.
"According to the president he’s the 'most overrated general,'" Short cracked in his intro. "I think he’s an American hero."
"I'm not just an overrated general. I’m the world’s greatest overrated general," joked Mattis, who received a standing ovation as he stepped to the dais. "I'm honored to be called that by Donald Trump, because he also called Meryl Streep an overrated actor. So I guess I’m the Meryl Streep of generals."
Mattis had said in an interview in August that his silence about Trump was "not going to be forever.”
One of the general's most biting jokes came in relation to Trump's infamous deferment of military service in Vietnam over alleged bone spurs in his feet.
"I earned my spurs on the battlefield; Donald Trump earned his spurs in a letter from a doctor," Mattis said.
He joked on Thursday that his work in combat zones overseas was easier than being in Trump’s Washington.
“I tried to bring some peace and order to the places with no organized government, chaotic and warring factions, irrational fears, and toxic hatred. It was hard work, but it wasn’t until I started working in Washington, D.C., that I realized how easy I had it overseas in the combat zone.”
He also knocked Trump for his many hours of executive time:
“It’s been a year since I’ve left the administration, the recovery process is going well," he joked. "The counselor says I’ll graduate soon. A year according to White House time is about 9,000 hours of executive time or 1,800 holes of golf."
Mattis, who has been critical of many of Trump's foreign policy decisions since leaving office, also got serious for a moment Thursday, mentioning the U.S.'s Kurdish allies in Syria. He called for the U.S. to again back the population, which has been attacked by Turkey.
"Let us restore trust in one another," Mattis said.
The president was onstage in Dallas at the same time as Mattis' keynote, delivering a campaign speech to a packed crowd at American Airlines Center.