The pop star has signed up to sing on the music mogul's star-studded cover version of the REM track 'Everybody Hurts', which will be the first time he has appeared on a record with his former bandmates in 15 years.
Robbie, 35, said: "I'm very honoured to be asked to contribute to the single. We can all do something to help the people of Haiti - and I urge everyone to do what they can."
The 'Bodies' singer quit the group - consisting of Gary Barlow, Jason Orange, Howard Donald and Mark Owen - in 1995.
Take That and Robbie are due to record their vocals in Los Angeles today (26.01.10), but it is not known whether they will be in the recording studio at the same time or if their voices will be added separately.
Producer John Shanks - who is behind the band's last two albums - is recording their efforts in the US, while fellow Take That producer Steve Robson is overseeing the track at London's Sarm studios.
The single - which aims to raise relief funds for the Caribbean island following their devastating earthquakes - will also see Robbie reunite with pop star Kylie Minogue, who Simon invited to appear on the track.
Robbie recorded the hit single 'Kids' with Kylie in 2000.
A source said: "Simon's delighted. Kylie's shown a real depth of understanding of what the single is all about. She's one of the biggest stars to say yes so far. It's a real coup."