Leinart spent four seasons with the Cardinals, primarily as backup for veteran Kurt Warner, whom he was supposed to succeed as starter.

In his first season, after a contentious negotiation making him the last member of the draft to sign a contract, Leinart agreed to a six-year, $51 million contract on August 14.
and not before Cardinal coach Dennis Green said that he had lost his patience.
Leinart played in the second quarter of the exhibition game against the New England Patriots on August 19.

Leinart started the fourth game of the season, in which he threw two touchdown passes.
During the previous week, Leinart was rumored to get the starting quarterback position after a poor performance by Kurt Warner in the previous game.
Coach Green even held a conference to state that Warner would still start that week's game.

In Week 6 against the 5–0 Chicago Bears, Leinart threw for two touchdown passes in the first half, but the Bears came back in the second half to win 24–23.

In a November 26 game, he set an NFL rookie record with 405 passing yards in a loss to the 6-10 Minnesota Vikings.
His quarterback rating was 74.0.
He suffered a sprained left shoulder (throwing arm) in a week 16 win over the San Francisco 49ers.
In 11 starts, Leinart threw for 2,547 yards and 11 touchdowns.
He finished the season with a 4–7 record.

Leinart opened the 2007 season on Monday Night Football against the San Francisco 49ers as the starting quarterback.
After a sequence of drives in which the offense stalled, head coach Ken Whisenhunt began to insert Warner as a situational quarterback.
On October 7, 2007, Leinart suffered a fractured left collarbone after being sacked by St. Louis Rams linebacker Will Witherspoon.
Three days later, he was placed on injured reserve, ending his season.
In his first two NFL seasons, Leinart had suffered two season-ending injuries within a period of five sacks.
With Warner at the helm for the remainder of the season, the Cardinals mounted a late-season surge and won five of their final eight games.

In Leinart's second season with Arizona, he started five games, completed 53.6% of his passes (60/112) and threw for 647 yards, 5.8 yards per attempt, two touchdowns and four interceptions.
His passer rating was 61.9.
He averaged 129 yards and 0.4 touchdowns per start.
In the 2008 offseason, after he recovered from the injury, Leinart was handed his starting job back, but his hold on the job was tenuous after another strong training camp performance by Warner.
Finally, after Leinart threw three interceptions within a matter of minutes versus the Oakland Raiders in the third preseason game, Warner was named the opening-day starter.
Leinart picked up only a limited number of snaps in mop-up duty behind Warner.
Warner started 16 games and took the Cardinals to their first ever Super Bowl, cementing his status as starter and Leinart's status as a backup.
For the 2008 season, he completed 15 of 29 passing attempts (51.7%), one touchdown, one interception, and an 80.2 passer rating.
In 2009, Leinart continued his role as back-up for Warner, who started all but one regular season game.

In 2010, Leinart was named the presumptive starter after Warner's retirement.
However, due to poor play, the starting job in training camp was given to Derek Anderson.
The Cardinals released Leinart on September 4, two days after the final preseason game, in favor of Anderson and rookies Max Hall and John Skelton.
Leinart spent four seasons with the Cardinals, primarily as backup for veteran Kurt Warner, whom he was supposed to succeed as starter.
In his first season, after a contentious negotiation making him the last member of the draft to sign a contract, Leinart agreed to a six-year, $51 million contract on August 14. and not before Cardinal coach Dennis Green said that he had lost his patience. Leinart played in the second quarter of the exhibition game against the New England Patriots on August 19.
Leinart started the fourth game of the season, in which he threw two touchdown passes. During the previous week, Leinart was rumored to get the starting quarterback position after a poor performance by Kurt Warner in the previous game. Coach Green even held a conference to state that Warner would still start that week's game.
In Week 6 against the 5–0 Chicago Bears, Leinart threw for two touchdown passes in the first half, but the Bears came back in the second half to win 24–23.
In a November 26 game, he set an NFL rookie record with 405 passing yards in a loss to the 6-10 Minnesota Vikings. His quarterback rating was 74.0. He suffered a sprained left shoulder (throwing arm) in a week 16 win over the San Francisco 49ers. In 11 starts, Leinart threw for 2,547 yards and 11 touchdowns. He finished the season with a 4–7 record.
Leinart opened the 2007 season on Monday Night Football against the San Francisco 49ers as the starting quarterback. After a sequence of drives in which the offense stalled, head coach Ken Whisenhunt began to insert Warner as a situational quarterback. On October 7, 2007, Leinart suffered a fractured left collarbone after being sacked by St. Louis Rams linebacker Will Witherspoon. Three days later, he was placed on injured reserve, ending his season. In his first two NFL seasons, Leinart had suffered two season-ending injuries within a period of five sacks. With Warner at the helm for the remainder of the season, the Cardinals mounted a late-season surge and won five of their final eight games.
In Leinart's second season with Arizona, he started five games, completed 53.6% of his passes (60/112) and threw for 647 yards, 5.8 yards per attempt, two touchdowns and four interceptions. His passer rating was 61.9. He averaged 129 yards and 0.4 touchdowns per start. In the 2008 offseason, after he recovered from the injury, Leinart was handed his starting job back, but his hold on the job was tenuous after another strong training camp performance by Warner. Finally, after Leinart threw three interceptions within a matter of minutes versus the Oakland Raiders in the third preseason game, Warner was named the opening-day starter. Leinart picked up only a limited number of snaps in mop-up duty behind Warner. Warner started 16 games and took the Cardinals to their first ever Super Bowl, cementing his status as starter and Leinart's status as a backup. For the 2008 season, he completed 15 of 29 passing attempts (51.7%), one touchdown, one interception, and an 80.2 passer rating. In 2009, Leinart continued his role as back-up for Warner, who started all but one regular season game.
In 2010, Leinart was named the presumptive starter after Warner's retirement. However, due to poor play, the starting job in training camp was given to Derek Anderson. The Cardinals released Leinart on September 4, two days after the final preseason game, in favor of Anderson and rookies Max Hall and John Skelton.
Matt Leinart