"I went for a run the other day and during it I started to think about the amount of effort that I have to put in this season and I just don't think I have the time to give to being a jockey any more," Murtagh said in the Racing Post.
"We have a lot on this season, with 24 new stables here and 45 horses riding out. I didn't want to give riding 30 percent and training 70 percent. All my life it has been 100 percent or nothing."
Murtagh rode more than 100 Group One winners and became top jockey at Royal Ascot for the fifth time in June.
He won the Derby at Epsom three times in six years with Sinndar (2000), High Chaparral (2002) and Motivator (2005).
Murtagh took out his training licence in May 2013.
(Reporting by Toby Davis; editing by Ken Ferris)
