In August 2014, Geraghty was cast as a series regular on the second season of the NBC procedural Chicago P.D., playing Sean Roman. In 2018, Geraghty starred in the TNT drama The Alienist, as NYPD Police Commissioner Theodore Roosevelt.
Geraghty's acting career took off when he joined the cast of the NBC police series Chicago P.D. as Sean Roman in August 2014. Two years later, he landed a starring role in the TNT drama The Alienist, playing a prominent NYPD figure, Theodore Roosevelt.