Okey had his contract selected by the Reds on Friday.
The 27-year-old was called up for his first taste of the majors with Tyler Stephenson heading to the injured list with a fractured thumb. Okey has a .265/.324/.441 slash line in 24 games for Triple-A Louisville this season, and he should serve as the Reds' secondary option at catcher behind Aramis Garcia while Stephenson is sidelined.