The 6-foot-4, 214-pound Ekblad played for Barrie in the Ontario Hockey League. He is the first defenseman to go No. 1 since St. Louis took Erik Johnson in 2006.
Without a clear-cut No. 1, Panthers general manager Dale Tallon was open to trading the pick. In the end, he decided to take the 18-year-old defenseman out of Belle River, Ontario.
The Panthers had a top-three pick in the NHL draft for the fourth time in the past five years. The first three — defenseman Erik Gudbranson (in 2010), wing Jonathan Huberdeau (2011) and center Aleksander Barkov (2013) — all played significant roles last season.
Florida also won the draft lottery in 2002 and 2003, but traded away those picks.
"We are thrilled to have selected Aaron with the No. 1 pick," Tallon said. "He is a strong, smart and physically mature defenseman who skates well and can play at both ends of the ice. Aaron is another building block for our team and we are confident that he will fit well with our young nucleus of talented players that includes Aleksander Barkov, Nick Bjugstad, Jonathan Huberdeau and Erik Gudbranson. We look forward to his continued growth and contributions to our team and the South Florida community."
Ekblad was the OHL's most outstanding defenseman last season, ranking first among defensemen with 23 goals and tying for fifth with 53 points. He also served as Barrie's captain.
The Sabres selected center Sam Reinhart with the second overall pick. He is the son of former NHL player Paul Reinhart, who was selected by the Atlanta Flames in the first round in 1979.
Reinhart has the potential to be a top-line center in filling a key need for the rebuilding Sabres, who are coming off one of their worst seasons in franchise history. Buffalo (21-51-10) finished last in the NHL standings, and set a franchise record for losses.
The Edmonton Oilers selected center Leon Draisaitl with the third overall pick, Calgary took center Sam Bennett with the fourth pick and the New York Islanders picked forward Michael Dal Colle fifth. Vancouver selected forward Jake Virtanen with the sixth pick, and Carolina took defenseman Haydn Fleury seventh.
There was a big trade in the hours before the draft, when the Anaheim Ducks acquired center Ryan Kesler from the Vancouver Canucks for center Nick Bonino, defenseman Luca Sbisa and the 24th overall pick Friday.
The 29-year-old Kesler is a standout two-way center who has spent his entire 10-season career in Vancouver, compiling six 20-goal seasons and 392 career points. The two-time U.S. Olympian won the Selke Trophy in 2011 as the NHL's best defensive forward.