The outcome never looked in doubt after the 27-year-old took the lead at the midway point.
Reflecting on his performance, the American revealed that he had done everything possible to take the pressure off himself.
"I'm happy with the win. I trained for this, very intensely," he told BBC Sport. "I do some ridiculous things. I was trying to treat this as much like a practice session as possible, where I have no pressure.
"I tried to relieve all pressure. The gold means everything and this is a dream come true."
Merritt had been competing in his first ever Games.