Henry Speight will join the Reds from the Brumbies at the end of the 2019 season, after agreeing a two-year deal to remain in Australia.
Fijian-born winger Speight, who earned the last of his 19 international caps for Australia in November 2017, has scored 45 tries in 119 Super Rugby appearances for the Brumbies.
"Whilst focused on the Brumbies for this season, I am delighted to be joining the Reds and I can't wait to meet both the team and the fans," said Speight, who cited family circumstances as a factor in his move to Brisbane.
"It's an exciting time in my life with [my partner] Louise and I expecting our first child and the opportunity to be around family is something we look forward to.
"I believe Australian rugby has a great future and I couldn't be happier to stay here and pursue my goals in Australian rugby with the Reds.
"I will be forever grateful for the Brumbies for giving me the chance to play Super Rugby at a club with an unbelievable culture and strong history. This was the toughest decision I have ever made."
The news comes as a blow to the Brumbies, who lost David Pocock this week as he confirmed his Super Rugby retirement.
"Henry is a legend of the Brumbies now and he always will be," said Brumbies coach Dan McKellar.
"Whilst it’s sad, we certainly understand why he has made the decision that he has, and we wish him all the best for the future."