The 26-year-old forward was a restricted free agent and avoided a salary arbitration hearing scheduled for Friday.
Mangiapane set NHL career highs in goals (35), assists (20) and points (55) in 82 regular-season games for the Flames last season. He had six points (three goals, three assists) in 12 Stanley Cup Playoff games.
"Obviously I'm excited that we could get a three-year deal done,'' Mangiapane said Wednesday. "I was getting nervous with the hearing approaching. I wanted a longer-term deal. I wanted to stay in Calgary longer."
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Selected by Calgary in the sixth round (No. 166) of the 2015 NHL Draft, Mangiapane has 132 points (78 goals, 54 assists) in 260 regular-season games, and 12 points (six goals, six assists) in 27 playoff games.
The Flames also avoided arbitration with Oliver Kylington; the defenseman signed a two-year, $5 million contract earlier Tuesday. A hearing was scheduled for Aug. 10.
Forward Matthew Tkachuk had a team-elected hearing scheduled, but was traded to the Florida Panthers on July 22 for forward Jonathan Huberdeau, defenseman MacKenzie Weegar forward prospect Cole Schwindt and a conditional first-round pick in the 2025 NHL Draft. The Panthers also received a fourth-round pick in the 2025 draft.
Calgary (50-21-11) finished first in the Pacific Division last season and lost to the Edmonton Oilers in the second round of the playoffs.
NHL.com staff writer Mike Zeisberger contributed to this report
