"He's the type of player you'd like to think could finish his career as a Cardinal," St. Louis chairman and CEO Bill DeWitt said Saturday.
St. Louis began contract talks with Carpenter in August. Both sides characterized the negotiations smooth.
"It was not one of those where we were sitting there debating all of Matt's faults or his weaknesses, because there weren't any," St. Louis General Manager John Mozeliak said. "He's really a special person not only on the field but off the field."
The deal includes a team option for a seventh year in 2020 at $18.5 million. Should the St. Louis decline the option, they would pay Carpenter a $2-million buyout.
"For a baseball junkie like myself, I can't think of a better place to play than the city of St. Louis," Carpenter said. "Busch Stadium, I still pinch myself every time I make that drive to the field.
"Playing in front of these fans, the city of St. Louis, Cardinal baseball as a whole, it's just so much fun. It's such a privilege to put on this jersey. It's something I don't take lightly at all."
Carpenter's agent, Bryan Cahill, said the 28-year-old received a $1-million signing bonus and will make $1.5 million this season. The salary escalates each year, reaching $14.5 million in 2019.
Carpenter hit .318 while leading the National League in hits (199), doubles (55) and runs (126) last season and playing mostly second base. He is moving back to third this season, where he has played most of his professional career.
He earned his first all-star selection in 2013 and finished fourth in MVP voting. A 13th-round draft choice out of TCU in 2009, Carpenter's first full season in the majors was 2012.
Carpenter switched to second during last spring training and started 128 games as a middle infielder in 2013. He also played 24 games at third.
Known in the clubhouse for his work ethic and daily preparation, it hasn't taken Carpenter long to take on a leadership role. He's made an impact not only on the younger Cardinals, but also on the veterans.
"They can't help but watch," Cardinals manager Mike Matheny said. "OK, how did this guy get on the board all of the sudden?
"How's he in the MVP running? Where did this come from? They can't help but translate the work that's put in and the discipline."
He fought back emotion at Saturday's press conference.
"I realize what a responsibility this is for me," Carpenter said. "I'm really looking forward to living up to this and continuing being part of such a great organization."