The 23-year-old, multiple golf-major winner is thought to have been in discussions with Nike over the proposed 10-year-deal for some time.
It has been reported the deal will be worth between $200m (£124m) and $250m (£155m) over 10 years. Specific details of the deal are unlikely to be announced.
The deal will be announced at the Abu Dhabi golf championships, where McIlroy and Tiger Woods are playing in the HSBC Championships.
Such a deal would trump Nike’s commercial partnership with Woods, who has been Nike's brand ambassador for the past 16 years.
McIlroy's previous endorsements deal with golf brand Titliest, Oakley, hotel chain Jumeirah, luxury watchmaker Audemars Piguet and Santander.
But Jumeirah has announced it will not be renewing its sponsorship deal with the world number one golfer. Titliest and Oakley have also said they will not be renewing their sponsorship deals with the player.
Nike and Horizon Sports, McIlroy's agent were both unavailable for comment.Follow @johnreynolds10