The 11-year NFL veteran beat out former first-round draft pick Matt Leinart, 25, who lost the job despite entering training camp as the expected starter, and playing significantly more in the pre-season.
Arizona plays its season-opener Sept. 7 against the San Francisco 49ers.
"Kurt has not had a lot of snaps with the first line and the first receivers in a game situation," Whisenhunt had said before the Cardinals' last pre-season contest Friday against the Denver Broncos.
Warner completed 12-of-17 passes in the pre-season for 142 yards, no touchdowns, no interceptions and a passing rating of 95.7.
Leinart, a Heisman Trophy winner at USC, completed 28 of 45 passes for 354 yards, two touchdowns, three interceptions and a 73.8 rating in the pre-season.