He left open the possibility that he would return, but stopped short of guaranteeing it.
He said the pressure of being one of the sport's biggest stars is always getting to him and that he needed a break to refresh.
"I have been fighting for a long time," St-Pierre said. "I have 22 fights in the UFC [actually 21] and 15 of my fights [actually 14] were for a world title. I have been fighting for a very long time at a high level and there is a lot of pressure, a lot of criticism. I've decided I need to take time off. I know the UFC is a business and they can't wait for my little personal [issue]. They have to keep things rolling so I have vacated my title out of respect to the other competitors.
"One day, when I feel like it, I might come back. But right now, I need a break."
St-Pierre, 32, has an overall mixed martial arts record of 25-2 and is 19-2 in the UFC and 12-2 in UFC title fights. He said his health is fine and that health issues did not factor into his decision.
St-Pierre, who won a highly controversial decision over Hendricks in his last fight, at UFC 167 on Nov. 16, said the decision has been coming for a while. In addition to the issues in his personal life, which he said he would keep private, he noted the pressure of trying to take the sport to the next level is immense.
He was the UFC's biggest pay-per-view star and it is believed that his two fights in 2013, against Nick Diaz at UFC 158 in March and against Hendricks last month, are the company's top selling pay-per-view shows of the year.
"The part people don't understand is, the situation I am in, is it's a lot of pressure," St-Pierre said. "Every fight I'm carrying weight on my shoulders. Every fight, it's like you add weight on my shoulders. Every fight, you add weight, you add weight and you add weight and at one point, it becomes so heavy I have a hard time carrying it myself.
"For me, in order to keep my mental equilibrium ... physically, I'm 100 percent. I'm still young and everything. I'm on top of the world. Mentally, I cannot go through another training camp right now. I don't know when I will be able to."
"If one day I feel ready, I'm going to come back," St-Pierre said, but added he would do so as the challenger.
White backed St-Pierre's decision and said he did not want anyone to fight unless they are fully committed to doing so.
"I agree with him 100 percent," White said. "If you aren't [100 percent], this isn't baseball or some sport where you go out. This is fighting, man. You have to be 100 percent mental, physical, emotional. If you're not, you should sit out and wait until you get your stuff cleared up. I think it's the right move."
- Mixed Martial Arts
- Martial Arts