The deal is worth $66.2 million, sources told ESPN.com's Pierre LeBrun, with an average of $8.275 million a year and a full no-movement clause.
Giroux still has one more year left on his current deal, so the new extension kicks in for the 2014-15 season.
"We are pleased to announce that we have agreed to an eight year contract extension with Claude Giroux," general manager Paul Holmgren said in a statement. "Claude is a high-quality young man that over the past few years has blossomed into our best player and also one of the top players in the league. We look forward to more and better things to come from Claude over the next number of years as we try to achieve our goal of becoming a championship team."
The deal comes with the Flyers reshaping a team that missed the playoffs last season.
A two-time 25-goal scorer, Giroux is the Flyers' top play-making offensive threat. He had 13 goals and 35 assists for 48 points in 48 games last season.
Overall, he has 291 points (91 goals, 200 assists) in 333 career games spread over six seasons in Philadelphia.
The Flyers have made several splashes the past two weeks. They landed this summer's most high-profile free agent by agreeing to terms with Vincent Lecavalier on a four-year contract Tuesday. Lecavalier was available after the Tampa Bay Lightning bought out the remaining years on his contract.
The Flyers announced Thursday that they will re-sign journeyman center Adam Hall to a one-year deal. The Flyers claimed Hall off waivers in April.
Information from The Associated Press was used in this report.