Golf returned to the Olympics for the first time in 112 years three years ago in Rio but McIlroy elected not to play due to concerns over the Zika virus.
The four-time major winner represented Ireland as a amateur but previously admitted he ‘resented' having to choose between Great Britain or Ireland in 2016.
"We are delighted that Rory has signalled his intention to compete for Ireland at the Olympics in Tokyo next year," said Neil Manchip, CGI nominee for men's golf team leader at the Tokyo Olympics.
"Having a multiple major winner as part of Team Ireland will, undoubtedly, be a boost to the entire team and I know he's excited about playing."
Justin Rose won Olympic gold for Great Britain in Brazil, where other high-profile players such as Adam Scott and Louis Oosthuizen also pulled out.
