Holbrook was discovered while working part-time as a carpenter for Jenny Wiley Theatre in Kentucky. He signed with Elite Models in 2001. He has worked for other agencies such as Wilhelmina Models. Holbrook has been a model for such designers and labels as Gucci, Jean Paul Gaultier, Versus, Hugo Boss, Bill Blass, Calvin Klein, Moschino, Marc Jacobs, DSquared².
Holbrook is also a Photographer who has done work for David Armstrong. He is also a Sculptor, and exhibited his work in his first art show, "Iscariot", at the Rare gallery in Chelsea, New York from April 19 to May 17, 2008.
In 2017, Holbrook played Donald Pierce, the antagonist in Logan, the sequel to The Wolverine.