In exchange, the Cardinals received minor league shortstop Rayder Ascanio, international cap space totaling $750,000 and cash considerations.
Leake will join a Seattle rotation that has struggled to produce quality outings over the past month while dealing with injuries to James Paxton and Felix Hernandez. Leake is 7-12 with a 4.21 ERA and is a proven veteran to add to Seattle’s rotation. But he has struggled since the All-Star break, going 1-5 with a 6.90 ERA in nine starts since July 14.
“Mike gives us an experienced starter that will help us as we navigate our way towards a playoff spot this season,” Mariners president and 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 under contract through the 2020 season with an option for 2021.
The deal comes before Thursday’s deadline for major league teams to acquire a player and have him be eligible for the postseason.
The Mariners (66-67) are three games out of the second wild-card spot in the American League. The Cardinals (66-65) are 5½ games out in the NL wild-card race.
In eight seasons, Leake has a career mark of 80-76 with a 4.02 ERA. He also has pitched for the Reds and Giants.
The 21-year-old Ascanio was hitting a combined .217 with nine home runs and 44 RBIs between stops at Class A Modesto, Double-A Clinton and Triple-A Tacoma.
It is the second trade involving the Mariners and Cardinals this summer. Seattle previously traded for Marco Gonzales.
The Associated Press contributed to this report.