The show explores the tense and demanding world of the police, paramedics, and firefighters as they confront terrifying and dangerous situations on the job, as well as day-to-day struggles in their private lives, reported Entertainment Weekly.
Britton, 50, joins the already-cast Angela Bassett and Peter Krause in her first role since she departed "Nashville" after five years on the country music show.
Murphy and Britton have previously worked together on "American Horror Story" and "The People v O J Simpson: American Crime Story".