Seattle also acquires cash and international slot money while sending 21-year-old middle infield prospect Rayder Ascanio to St. Louis.
The Seattle rotation has been hit hard by injuries this season, with top starters Felix Hernandez and James Paxton both currently on the disabled list. Hisashi Iwakuma and Drew Smyly are also injured.
“Mike gives us an experienced starter that will help us as we navigate our way towards a playoff spot this season,” Mariners general manager Jerry Dipoto said in a statement. “As one of the most durable starters over most of the last decade, he’ll be a valuable addition for not just the near future, but for seasons to come.”
Leake is owed at least $48 million over the next three seasons, in addition to about $2 million for the rest of this year. He has a mutual option for the 2022 season that includes a $5 million buyout if the team doesn’t pick it up.
Leake, who waived his no-trade clause to complete the deal, has a 4.21 ERA and 1.325 WHIP in 26 starts this season.
The Mariners and Cardinals are both currently on the periphery of their leagues’ Wild Card races.