The actor will appear in one episode of the show when it returns to USA, Entertainment Weekly reports.
He is expected to play a trial attorney who is hoping to expand his legal empire.
Moses has previously starred as Paul Young on Desperate Housewives and Duck in Mad Men.
Moses also recently signed up for a guest role in a December episode of TNT's The Closer.
Fairly Legal was renewed for a second season in May, but some creative changes are expected to be made to the show.
A premiere date for the second season has not yet been announced.