Financial terms were not released.
The 24-year-old forward has an NHL career high 20 goals and 33 points in 59 games this season. He agreed to a one-year contract June 29, 2018 and could have become a restricted free agent July 1.
"We're thrilled that Frank will be part of the Florida Panthers organization for the next three years," general manager Dale Tallon said. "At a young age, Frank has the work ethic, scoring sense and two-way ability to complement any of our forward lines and we look forward to working with him as he continues his development with our club."
Acquired in a trade with the Boston Bruins on Feb. 22, 2018, Vatrano has 72 points (45 goals, 27 assists) in 183 regular-season games, and one goal in six Stanley Cup Playoff games. He was signed by the Bruins as an undrafted free agent March 13, 2015.
The Panthers (27-25-8) are 10 points behind the Carolina Hurricanes for the second wild card into the playoffs from the Eastern Conference.
