Ekblad, 18, was the No. 1 pick at the 2014 NHL Draft. He was named the Ontario Hockey League's most outstanding defenseman last season, and ranked first among the league's blueliners with 23 goals and tied for fifth with 53 points (23 goals, 30 assists) for the Barrie Colts.
The 6-foot-3, 213-pound Ekblad became the third player in his 18-year-old birth year to earn the OHL's most outstanding defenseman honor in the past 20 years, following Ryan Ellis (Nashville Predators) in 2009 and Bryan Berard in 1995. He also served as Barrie's team captain.
"We are very pleased to have signed Aaron," Panthers general manager Dale Tallon said in a statement. "He is a talented, strong, smart and hardworking defenseman who is ready to take the next step in his professional career. We look forward to watching him compete and develop at our prospects camp, throughout our main training camp and in preseason competition."
The Belle River, Ontario, native played as a 17-year-old for Canada at the 2014 World Junior Championship. He had one goal and one assist in seven games.