The Pirates will call up Contreras from Triple-A Indianapolis to start Wednesday against the Cubs, Jason Mackey of the Pittsburgh Post-Gazette reports.
The move was rumored earlier in the day Tuesday but has since been confirmed. The 21-year-old has had an impressive season in the upper minors, striking out 35 percent of opposing batters and walking just 5.6 percent en route to a 2.64 ERA, though just one of his 13 starts came at the Triple-A level.