Tournament organisers announced the American's commitment to the Feb. 5-8 event and Johnson on Saturday told Golfweek magazine it was time for him "to grow up" and get back to competitive golf.
Johnson's unexpected absence began after the Canadian Open in late July and he said he has since been working hard with a team of top clinicians, including a life coach.
"I try not to get too emotional, whether it's going really well or going really bad," Johnson, an eight-times winner on the PGA Tour, said. "I always try to stay even keel -- which is great for golf, but it isn't always great for life.
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"I knew I wasn't happy, but until I started talking through it and working with some of the people that I did, I didn't really realize it. It's been a huge help, a huge relief, understanding that.
"It was time to grow up," he said. "I'm feeling good. I can't go out and say 'I'm going to win this tournament', but I just want to compete and put myself in position to have a chance."
When Johnson announced his decision to step away from golf, rumours about his lifestyle swirled, prompted by a Golf.com article alleging he had been suspended by the PGA Tour for six months after a third failed drug test, and a second for cocaine.
The PGA Tour, which had initially said it did not comment on rumours or speculation, released another statement a few hours later saying that Johnson had taken a voluntary leave of absence and had not been suspended.
Earlier this week, Johnson told ESPN that drugs "didn't really have a role in my life" and that his main weakness had been vodka.
"(I) would drink and drink to excess," the 30-year-old said, adding that "the change I made is, I just don't do that any more".
Johnson plans to play in three PGA Tour events next month. He celebrated the arrival of his first child when his fiancee, Paulina Gretzky, gave birth to a son on Monday.
"My life has already changed," Johnson said. "There's nothing better (than fatherhood)."
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