In 2010–11, Ekblad competed for the Sun County Panthers minor midget AAA team in Belle River, Ontario. He had 34 points in 30 regular season games and added 21 points in 18 playoff games. He captained the team and lead them to an alliance championship.
Ekblad’s application to be the only player born in 1996 in the draft was approved unanimously, after a six-week review by Hockey Canada. With the approval, Ekblad became the first defenceman ever granted "exceptional player" status. The status allowed him to compete in the Canadian Hockey League a year earlier than his eligible age. The only other players to have been given such eligibility are centre John Tavares in 2005, Connor McDavid in 2012, Sean Day in 2013, and Joseph Veleno in 2015.
In the 2014 OHL Coaches Poll, the results of which were released in Toronto, he won top honours in four different categories in the Eastern Conference of the Ontario Hockey League, earning first-place finishes for best shot, hardest shot, best offensive defenceman, and best defensive defenceman. He was also voted second in the category of best penalty killer, behind Oshawa Generals forward Scott Laughton.
Ekblad was selected first overall in the 2014 NHL Entry Draft by the Florida Panthers on June 27, 2014. He subsequently signed his first NHL contract on September 3, a three-year, entry-level deal with the Panthers. After making the Panthers' opening night roster out of training camp for the 2014–15 season, Ekblad made his NHL debut on October 9 against the Tampa Bay Lightning. In the game, he scored his first career NHL point, an assist on a Jonathan Huberdeau goal, in Florida's eventual 3–2 loss in overtime. Ekblad later scored his first career NHL goal on November 1 against Steve Mason of the Philadelphia Flyers in a 2–1 Panthers win.
On December 6, in a game against the Buffalo Sabres, Ekblad scored a career-high three points in a 3–2 Panthers victory, the first Panthers rookie to record a three-point game since Dan Boyle during the 1998–99 season. Ekblad was also named the game's first star for his performance. On January 23, 2015, Ekblad was named as an injury replacement for Colorado Avalanche defenceman Erik Johnson at the 2015 NHL All-Star Game in Columbus, Ohio. In the Game, Ekblad recorded four assists in Team Toews' 17–12 victory over Team Foligno.
Ekblad finished his rookie season with 12 goals and 27 assists (39 points) in 81 games played for Florida. Following the conclusion of his rookie season, Ekblad led all rookie defencemen in goals, power play goals (6), power play points (13), shots (170) and fewest shot attempts against per 60 minutes (38.04). He also finished second in assists, plus-minus (+12), hits (109) and blocked shots (80), while also averaging 21:48 of ice time per game. On April 23, Ekblad was named one of three finalists for the Calder Memorial Trophy — awarded annually to the NHL's rookie of the year — along with the Ottawa Senators' Mark Stone and Calgary Flames' Johnny Gaudreau. On June 24, 2015, Ekblad was announced as the Calder winner.
On July 2, 2016, Ekblad and the Panthers agreed to an eight-year, $60 million extension.
During Team Canada junior team's training camp in August 2014 in preparation for the upcoming 2015 World Junior Ice Hockey Championships in December 2014, Ekblad suffered a concussion in an exhibition game against the Czech Republic.
Ekblad played for Canada at the 2015 World Championships, where they won the gold medal for the first time since 2007 with a perfect 10-0 record.
Ekblad's brother Darien, a goaltender, was drafted into the OHL by the London Knights. Aaron Ekblad attended St. Anne's Catholic High School and was an honour roll student in the WECDSB. Ekblad was born in Windsor, but grew up in Belle River, Ontario. His great-grandfather was Swedish, hence the last name "Ekblad".