In 1998, Calvillo signed as a free agent with the Montreal Alouettes, where he became one of the most outstanding quarterbacks in history.
He led the Alouettes to the 2002 Grey Cup, their first in 25 years, where he was named the most valuable player in the game.

During the 2003 CFL season, Calvillo broke numerous Montreal Alouette passing records, completing 408 of 675 passing attempts for 5,891 yards and 37 touchdowns.
In 2004, with 6,041 passing yards, Calvillo became the fourth quarterback in CFL history to pass for more than 6,000 yards in a single season (Doug Flutie, David Archer, and Kent Austin being the other three), earning him the East Division nomination for Most Outstanding Player for the third consecutive year.
With Calvillo quarterbacking the Alouettes' offence, the 2004 Alouettes became the first team in CFL history to have four players with over 1,000 yards receiving in the same season: Ben Cahoon (1183 yards), Jeremaine Copeland (1154 yards), Thyron Anderson (1147 yards), and Kwame Cavil (1090 yards).
In 2005, Calvillo and the Alouettes repeated the feat of four receivers over 1,000 yards: Kerry Watkins (1364 yards), Terry Vaughn (1113 yards), Ben Cahoon (1067 yards), and Dave Stala (1037 yards).

The 2008 CFL season saw Calvillo hit a number of career milestones.
On June 26, in a game against the Hamilton Tiger-Cats, Calvillo surpassed Danny McManus to become the second-all-time leading passer in the CFL.
On July 31, in another game against the Hamilton Tiger-Cats, Calvillo became the fourth quarterback in league history to reach 300 career touchdown passes.
On August 15, 2008, in a game against the Toronto Argonauts, Calvillo became the second quarterback in CFL history after Damon Allen to reach 4,000 career pass completions.
With 5,633 passing yards and 43 touchdown passes, Calvillo won the 2008 Most Outstanding Player award.
Calvillo led the Montreal Alouettes to the 2008 Grey Cup final, which the Alouettes lost 22-14 to the Calgary Stampeders.

In 2009, Calvillo added to his club records while reaching more CFL milestones.
On July 23, 2009, he surpassed Canadian Football Hall of Famer Ron Lancaster's 334 career touchdown passes to move into second place all time.
 He sat out two games during the regular season, but still accumulated 4639 yards while posting a remarkable 72.0% completion rate, the second best single-season completion rate in CFL history behind Dave Dickenson's 73.98% mark set in 2005.
Calvillo led Montreal to a 16-point fourth quarter comeback victory in the 97th Grey Cup on Nov. 29, when the Alouettes defeated the Saskatchewan Roughriders 28-27 on a last-second field goal known as the "13th Man" finish.

Calvillo won his third Grey Cup on November 28, 2010, at 98th Grey Cup in Edmonton, Alberta where he defeated the Saskatchewan Roughriders 21-18 for the second year in a row.
He added to his record total of passing yards in Grey Cup games with 2470 yards, as well as setting the record for Grey Cup starts with eight.
As of the 2010 CFL season, Calvillo is 3-5 in Grey Cup Championship Games.

In a post-game interview, he revealed that he would be undergoing off-season surgery to remove a lesion on his thyroid that was discovered after he injured his sternum during the season.
On December 21, 2010, it was reported that Calvillo had successful thyroidectomy surgery to remove a cancerous lesion.

On July 15, 2011, in a game against the Toronto Argonauts, Calvillo completed his CFL record 395th career touchdown pass to Éric Deslauriers.
On August 4 of that same season, and again against the Argonauts, Calvillo completed his 5159th pass completion to Brandon London to move past Damon Allen to become the leader in that category as well.
Then, on October 10, 2011, Calvillo completed a touchdown pass to Jamel Richardson to become professional football's all-time leading passer, in the Alouettes' third and final game against the Toronto Argonauts that year.
 In 2012, Calvillo became the only player in football history to pass 5,000 yards seven times in his career.
He reached 4,000 yards passing
In 1998, Calvillo signed as a free agent with the Montreal Alouettes, where he became one of the most outstanding quarterbacks in history. He led the Alouettes to the 2002 Grey Cup, their first in 25 years, where he was named the most valuable player in the game.
During the 2003 CFL season, Calvillo broke numerous Montreal Alouette passing records, completing 408 of 675 passing attempts for 5,891 yards and 37 touchdowns. In 2004, with 6,041 passing yards, Calvillo became the fourth quarterback in CFL history to pass for more than 6,000 yards in a single season (Doug Flutie, David Archer, and Kent Austin being the other three), earning him the East Division nomination for Most Outstanding Player for the third consecutive year. With Calvillo quarterbacking the Alouettes' offence, the 2004 Alouettes became the first team in CFL history to have four players with over 1,000 yards receiving in the same season: Ben Cahoon (1183 yards), Jeremaine Copeland (1154 yards), Thyron Anderson (1147 yards), and Kwame Cavil (1090 yards). In 2005, Calvillo and the Alouettes repeated the feat of four receivers over 1,000 yards: Kerry Watkins (1364 yards), Terry Vaughn (1113 yards), Ben Cahoon (1067 yards), and Dave Stala (1037 yards).
The 2008 CFL season saw Calvillo hit a number of career milestones. On June 26, in a game against the Hamilton Tiger-Cats, Calvillo surpassed Danny McManus to become the second-all-time leading passer in the CFL. On July 31, in another game against the Hamilton Tiger-Cats, Calvillo became the fourth quarterback in league history to reach 300 career touchdown passes. On August 15, 2008, in a game against the Toronto Argonauts, Calvillo became the second quarterback in CFL history after Damon Allen to reach 4,000 career pass completions. With 5,633 passing yards and 43 touchdown passes, Calvillo won the 2008 Most Outstanding Player award. Calvillo led the Montreal Alouettes to the 2008 Grey Cup final, which the Alouettes lost 22-14 to the Calgary Stampeders.
In 2009, Calvillo added to his club records while reaching more CFL milestones. On July 23, 2009, he surpassed Canadian Football Hall of Famer Ron Lancaster's 334 career touchdown passes to move into second place all time.  He sat out two games during the regular season, but still accumulated 4639 yards while posting a remarkable 72.0% completion rate, the second best single-season completion rate in CFL history behind Dave Dickenson's 73.98% mark set in 2005. Calvillo led Montreal to a 16-point fourth quarter comeback victory in the 97th Grey Cup on Nov. 29, when the Alouettes defeated the Saskatchewan Roughriders 28-27 on a last-second field goal known as the "13th Man" finish.
Calvillo won his third Grey Cup on November 28, 2010, at 98th Grey Cup in Edmonton, Alberta where he defeated the Saskatchewan Roughriders 21-18 for the second year in a row. He added to his record total of passing yards in Grey Cup games with 2470 yards, as well as setting the record for Grey Cup starts with eight. As of the 2010 CFL season, Calvillo is 3-5 in Grey Cup Championship Games.
In a post-game interview, he revealed that he would be undergoing off-season surgery to remove a lesion on his thyroid that was discovered after he injured his sternum during the season. On December 21, 2010, it was reported that Calvillo had successful thyroidectomy surgery to remove a cancerous lesion.
On July 15, 2011, in a game against the Toronto Argonauts, Calvillo completed his CFL record 395th career touchdown pass to Éric Deslauriers. On August 4 of that same season, and again against the Argonauts, Calvillo completed his 5159th pass completion to Brandon London to move past Damon Allen to become the leader in that category as well. Then, on October 10, 2011, Calvillo completed a touchdown pass to Jamel Richardson to become professional football's all-time leading passer, in the Alouettes' third and final game against the Toronto Argonauts that year.  In 2012, Calvillo became the only player in football history to pass 5,000 yards seven times in his career. He reached 4,000 yards passing 
Anthony Calvillo