Merritt, who was told he would never run again after being diagnosed with kidney disease in 2013, set the second fastest time behind compatriot David Oliver in the heats of the 110 metres hurdles on Wednesday.
The disease, caused by a rare genetic disorder found predominantly in African Americans, has damaged his organ to such an extent that he will receive one of his sister’s kidneys in Arizona on Sept. 1.
“I’m here for mental sanity more than anything,” he told reporters.
“I don’t want to be sitting in my house awaiting surgery, I’d rather be out enjoying life to the fullest.
“Who knows? This could potentially be my last championship if things don’t go well. But I’m optimistic that I’ll be back and able to train for the Rio Olympics.”
Merritt had a brilliant 2012, winning gold at the London Olympics and shattering the world record with a time of 12.80 seconds at the Brussels Diamond League meeting the following month.
It was after he finished sixth at the 2013 world championships that his illness was diagnosed.
“When they told me I’d never run again, my whole world ended in my mind,” he added.
“That I am here again running shows me that I’m a fighter and that I can overcome anything if I stay with a positive mind.
“For this championships, I’m going to take it one race at a time.”
Merritt ran 13.25 seconds to win his heat on Wednesday morning to qualify for Thursday’s semi-finals and said he was glad to have the news about the transplant out in the open.
“Just to be keeping that secret, it felt like a weight had been lifted when I was able to share it,” he said.
“The positive outreach has been amazing. I love running, I love competing, this is my life and here I am.”
(Reporting by Nick Mulvenney, editing by Amlan Chakraborty)