Gordon withdrew with a hip injury on Monday.
Mitchell told reporters on Monday that he received the news on Sunday night.
"When I found out, I was excited," Mitchell told reporters. "I have a couple of ideas. I've been googling YouTube and watching old dunk contests. I'm definitely excited to participate."
Mitchell, 21, has exploded into the NBA as a rookie this season, shoulder to shoulder with Philadelphia's Ben Simmons in the Rookie of the Year race. He's shown a penchant for explosive dunks and could fare well in the event.
Mitchell is averaging 19.7 points, 3.5 assists and 3.4 rebounds per game for Utah. He's had two 40-plus-point performances.
Gordon, who leads the Magic with 18.4 points per game average this season, has missed the team's past three games with his injury.
Gordon had competed in the past two All-Star dunk contests and finished as runner-up in 2016. He was eliminated in the first round last year.