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.
In 2017, Holbrook played Donald Pierce, the antagonist in Logan, the sequel to The Wolverine.