The 23-year-old world number one was unveiled as the company's new brand ambassador in Abu Dhabi on Monday.
Although the exact details of the contract were not announced, it has been widely reported to be worth as much as $150m over 10 years, if McIlroy carries on winning majors.
"I chose Nike for a number of reasons," said the Northern Irishman.
"It's a company and a brand that really resonates with me. It's young. It's athletic. It's innovative. They are committed to being the best, as am I."
Signing with Nike is another step towards living out my dream
McIlroy, previously with Titleist, will now use Nike's full range of clubs, balls, clothing and accessories as he joins 14-major winner Tiger Woods in the company's colours.
The champion golfers go head to head in Nike's new advert, which shows them teeing off on a golf course with some unexpected results.
McIlroy challenges Woods, who he refers to as "the old guy" as their golf balls bounce into homes, offices and even interrupt one couple's big day.
While McIlroy chuckles that he is having "one of those days" when he "just can't miss", Tiger has the last laugh.
Cindy Davis, president of Nike Golf, said: "Rory is an extraordinary athlete who creates enormous excitement with his on-course performance while, at the same time, connecting with fans everywhere.
"He is the epitome of a Nike athlete and he is joining our team during the most exciting time in Nike Golf's history. We are looking forward to partnering with him to take his remarkable career to the next level."
McIlroy tweeted he was "pumped to officially be a Nike athlete" and was welcomed to the fold by fellow Nike-sponsored sportsman Wayne Rooney, who said: "Excited to see you have another great season."
McIlroy, who already has two major titles under his belt, begins the new season this week at the Abu Dhabi HSBC Championship.