Martin, 42, is the first actor to join the pilot from the Desperate Housewives creator.
The project is centered on Hallelujah, Tenn., a town being torn apart by forces of good and evil. A stranger arrives to restore justice and faith to its residents. Episodes will be feature songs sung by the gospel choir, serving as a type of Greek chorus.
Martin is best known his nine-year stint on Law & Order as Det. Ed Green, as well as his work in the original Broadway production of Rent.