The singer, whose album Reality Killed The Video Star is expected to top the charts this weekend, will reportedly perform with the group for a Children In Need charity spectacular on Thursday night.
It will be the first time in 14 years he has performed with Mark Owen, Jason Orange, Howard Donald and Gary Barlow, who is organising the event.
A source told The Sun on Wednesday: "The reunion is go. Robbie is utterly thrilled about it. He's been dreaming of performing with Take That again for years and now it's going to happen.
"They haven't decided what they are going to sing together, but something will take shape in rehearsals today."
Paul McCartney is also expected to perform at the event, which will take place at London's Royal Albert Hall.
Robbie left Take That in 1995 and had a public falling out with the outfit's songwriter Gary. But the two put aside their differences in 2005 and have recently been working together on new material.