[3] Nagle was born in Eugene, Oregon, then raised in DeKalb, Illinois,[4] and in Williamsburg, Virginia.

He graduated from Lafayette High School in Williamsburg in 1988, and from Northwestern University in 1992,[5] with a double-major in theatre and philosophy.

He has been married since October 7, 1995, to Heather Allyn,[6] who works as a casting director in reality television and has been nominated for multiple Emmy and Artios awards.

He is known for his performances in Good Trouble, NCIS: Los Angeles, Batwoman, Dynasty, Safety, To Hell and Gone, Superior Donuts, Bad Samaritan, The Librarians, Fishing Naked, Grey’s Anatomy, Criminal Minds, New Year’s Eve, Mad Men, Eli Stone, Cold Case, Everwood, Buffy the Vampire Slayer, The Guardian, and Dawson’s Creek.

[20] In 2018, Rob won Los Angeles Drama Critics Circle Award for his Featured Performance in The Little Foxes at Antaeus Theatre Company.