O’Donnell is “completely thrilled” to be making her debut at Carols, after many years spent watching Gleeson, who has performed at the event five times.
“I enjoy it because we know each other so well so from a musical point of view, it is so lovely being able to work on things,” she said.
“I also really admire Simon as a performer so I love the fact that I get to watch him do his thing right up close to him on stage.”
The duo met at acting school in Western Australia and grew up performing together before they were together as a couple.
But they rarely get the chance to perform together because someone has had to stay at home in Geelong to look after their 13-year-old daughter Molly and eight-year-old son Raf.
Molly and Raf will be watching the performance from the bowl, alongside O’Donnell’s parents.
“They are super excited,” said O’Donnell.
“It is just such a beautiful night on and off stage. It is just a gorgeous atmosphere and such a lovely way to spend the day together as a family [whether] you are in the audience or you are performing.”
The couple will be performing alongside the popular Australian entertainer Silvie Paladino.
“It is hard to go past her without welling up,” said O’Donnell.
“When you sing with Silvie you have to bring your A-game because she will just blast you off the stage,” added Gleeson.
There are also a number of musical casts performing this year from productions such as Chicago, Come From Away and Harry Potter and the Cursed Child – all of which are playing in Melbourne.
“I’m looking forward to what the cast brings because they always bring a flavour of something of their show to their performance,” Gleeson said.
Gleeson and O’Donnell have a series of joint performances booked for early 2020.
“I really hope this particular performance goes well because it’s a litmus test for us,” said Gleeson.
The song they’ll be singing is a well-kept secret, with all to be revealed on Tuesday evening
Nine is the owner of ‘The Age’.