ESPN reported that the contract is worth a total of $28 million.
Stastny comes to St. Louis from the Colorado Avalanche, the sole team he's played for since coming into the league in 2006. The 28-year-old notched 25 goals and 35 assists for the Avalanche last season and tied for the team lead with 10 playoff points.
It's an important addition for the Blues, especially since it helps weaken Colorado, which finished one point ahead of St. Louis for the Central Division title last season.
Stastny will become the third member of his family to suit up for the Blues. His brother, Yan, played for the franchise from 2007-10, while his father, Peter, played the final two seasons of his Hall of Fame career in St. Louis from 1993-95.