M. Reilly was a Human Starfleet officer in the 22nd century.

In 2154, he was listed as a Propulsion Systems officer on the dedication plaque of the Columbia NX-02. (ENT: "Affliction", dedication plaque)

In January of 2155, he was listed as an Instrumentation and Control officer on the directory placards at Starfleet Command's Fleet Operations Center, Sol Sector. His office was located in room #1331. (ENT: "Demons", directories)

This character was only mentioned in writing.
He was named after Enterprise Steadicam assistant Mark Reilly.