The Cardinals claimed their 10th Major League Baseball championship by winning the best of seven series final 4 games to 1, ending the franchises longest title drought since its first title back in 1926.
"We shocked the world," Cardinals slugger Jim Edmonds said.
In winning the title, St Louis became the club with the worst regular season record to win the World Series after thy scrapped into the playoffs with a 83-78 regular season record.
"We were warriors."
"Thank God we proved everybody wrong," St. Louis star Albert Pujols said.
"We never gave up. We were warriors."
Weaver, a 30-year-old US right-hander who spent his first 3 1/2 seasons with the Tigers, confounded Detroit batters for eight innings, allowing only one earned run on four hits while his teammates took advantage of some more Tigers errors.
He was 3-10 when he came to the Cardinals from the Los Angeles Angels in June but form some form by the end of the season and pitched the game of his life when it mattered most.
"Everything fell into place. These guys I play around are incredible," Weaver said. "I just wanted to make it come true for them."
The Cardinals took what was to be a match winning lead with two runs in the fifth inning thanks to a clanger from Detroit rookie Jason Verlander, the fifth error by a Tiger pitcher in as many games.
Adam Wainwright is mobbed
St Louis David Eckstein was named the World Series' Most Valuable Player after batting .364 (6-for-9) and driving in four runs in the final two games.
"We believed in ourselves," Eckstein said.
"This isn't just mine. It is everybody's. It was a total team effort."
St. Louis sealed the victory in the seventh inning as Scott Rolen stretched his playoff hit streak to 10 games with a two-out single to score Eckstein from second base and produce the final margin.
Cardinal closing relief pitcher Adam Wainwright entered in the ninth inning and gave the Tigers a consolation run through a one-out double to Sean Casey.
However the final pitch sparked a celebration by players on the field and a crowd of 46,638 in the grandstands.
La Russa joins club
Cardinals manager Tony La Russa became only the second man to guide teams from the American and National leagues to World Series crowns after this year’s title joins his one he won with Oakland in the 1989 title.
La Russa joins former Detroit manager Sparky Anderson.
"I'm feeling so great for our team. We went through so much. We wanted it so bad," La Russa said.
"We had so many players who had never won a ring. I'm just bursting. This is an experience I will never forget. It's the greatest."
Stacks on the mill: the Cardinals
celebrate in traditional style
The Tigers were denied their first World Series title since 1984 after a season in which they snapped a run of 12 years without a winning record, including an American League-record 119 losses in 2003.
"We just didn't play good enough," Tigers manager Jim Leyland said.
"They just played better than we did. We didn't play good enough to win a World Series. I just hope people remember where we came from."
Detroit became the first team since 1979 to make errors in the first five games of a World Series.