The All My Children star will play Charlie in the Sarah Michelle Gellar drama, according to TV Guide.
The character will meet recovering addict Bridget (Gellar) at a Narcotics Anonymous meeting and will step up when her sponsor (Mike Colter) is unavailable.
Miller currently plays Billy Abbott on CBS soap opera The Young and the Restless and has also appeared in episodes of Justified and CSI: NY.
He will make his Ringer debut in the show's fifth episode. Other actors confirmed to appear on the series include fellow Young and the Restless star Michelle Stafford, All My Children's Justin Bruening and The Suite Life on Deck's Zoey Deutch.
Ringer's executive producers Eric Charmelo and Nicole Snyder recently promised that fans will be "shocked" by the show.
Ringer premieres on Tuesday, September 13 at 9/8c on The CW. The show will air on Sky Living in the UK.
> Sarah Michelle Gellar: 'I'm enjoying shooting Ringer'
Wattch a trailer for Ringer below: