[9] After being passed over in the 2004 Ontario Hockey League (OHL) draft,[10] Giroux played for the Cumberland Grads during the 2004–05 season at age 16.

Despite missing most of the season after contracting mononucleosis, Giroux scored 40 points across 48 games and was named the Canadian Junior Hockey League (CJHL)'s Rookie of the Year.

[9] A free agent, Giroux was invited to the Quebec Major Junior Hockey League (QMJHL)'s Gatineau Olympiques training camp for a walk-on tryout.

[12] Giroux made his NHL debut when the Flyers visited the Ottawa Senators on February 19, 2008, recording no points and being the team's first shooter in the shootout.

[14] After a disappointing training camp for the Flyers at the beginning of the 2008–09 season, Giroux was assigned to the team's American Hockey League (AHL) affiliate, the Philadelphia Phantoms.

After acclimatizing to professional hockey, however, things turned around quickly; he was named Rookie of the Month for December for his eight goals and six assists in eight games played.

His first Stanley Cup playoff goal came in a 6–3 win in Game 3 of the 2009 Eastern Conference Quarterfinals against Marc-André Fleury of the Pittsburgh Penguins.

Giroux spent a large amount of time centering James van Riemsdyk, the highly touted rookie winger that the Flyers had drafted second overall in 2007.

The Flyers' fortunes, however, soon turned dramatically: they qualified for the 2010 playoffs on Giroux's game winning goal in a shootout against the New York Rangers.

The Flyers made an historic comeback from three games to none down against the Boston Bruins to win the next four and advance to the Eastern Conference Final, where they dominated the Montreal Canadiens.

[16] After the Flyers traded away Jeff Carter and Mike Richards in the 2011 off-season, Giroux took over the role as first line centre for the club.

[18] On May 7, 2012, Giroux received a one-game suspension for a hit to the head of New Jersey Devils forward Dainius Zubrus during Game 4 of the Eastern Conference Semi-finals.

[4] After the Flyers' elimination, Giroux had surgery on both of his wrists; the right to repair torn cartilage, and the left to remove bone spurs.

[21] At the time news of the surgery was revealed, Giroux was still the playoffs' leading point scorer, even though his team had been eliminated two weeks earlier.

[22][23] During the 2012–13 NHL lock-out, Giroux and Flyers teammate Daniel Brière played for Eisbären Berlin of the German Deutsche Eishockey Liga (DEL).

After the lock-out ended, Giroux was named the 19th team captain in Flyers history on January 15, 2013, taking over for the indefinitely-injured Chris Pronger.

[27] From February 12 through the end of the regular season, Giroux was the fourth-most productive player in the League, scoring ten goals and 30 assists for a total of 40 points during that span.

At the conclusion of the season, Giroux was nominated for the NHL's Hart Trophy and the Ted Lindsay Award, both of which he lost to Sidney Crosby.

[35] This also made him the first Flyers skater since John LeClair and Eric Lindros to be selected for the All-Star Game roster five or more times.

[41] Giroux helped the Flyers qualify for the 2018 Stanley Cup playoffs, where he recorded 3 points in 6 games in an eventual first round loss to the Pittsburgh Penguins.

[46] He is the tenth active player to achieve 600 assists, and his points total surpassed Hall of Famer Bill Barber for second overall in Flyers' franchise history.

[47] With the Flyers having a poor 2021–22 season and his contract approaching expiration, the possibility of Giroux being traded in advance of the 2022 Stanley Cup playoffs became a major point of discussion in sports media.

He was presented with a silver stick at a pre-game ceremony by Bobby Clarke, and named the first star of the game despite not registering a point.

[55] He scored his first goal with his new team in an April 5 game against the Toronto Maple Leafs, where the Panthers rallied to a 7–6 victory in overtime after a 5–1 deficit in the second period.

Giroux played a pivotal role in the series-clinching win in Game 6 against the eight-seeded Capitals, leading the team past the first round for the first time in a quarter century.

[58] In the second round matchup against the two-time defending Stanley Cup champion and fifth-seeded Tampa Bay Lightning, the Panthers were swept in four games, bringing the postseason run to an end.

[68] During the 2012–13 lockout, Giroux also made a voice appearance in the 2012 TV film, The Magic Hockey Skates (based on the book of the same name).

[74][75][76] In May 2023, Giroux was given a sponsor's exemption to play in the professional golf PGA Tour Canada event Commissionaires Ottawa Open and was also the tournament's honorary chair.