The married couple, who starred in Harry Potter and Downton Abbey respectively, will appear alongside performers including actresses Minnie Driver and Rosalie Craig, as well as Hamilton actor Giles Terera.
The performance, which has been organised by the Donmar Warehouse theatre, will be broadcast from St Paul's Church in Covent Garden in central London and will feature musical numbers, sketches and seasonal poetry.
Donmar Warehouse artistic director Michael Longhurst said: “At the end of a very difficult year for us all, we wanted to bring together a group of incredible artists to celebrate the festive season in true Donmar style.
“We are thrilled to be creating this concert for the special setting of the Actors’ Church – and offer it as a heartfelt thank you to our audiences for their unwavering support this year.
“Even though we can’t be together in person, we hope you will all join us online to share the joy of music and theatre which has endured throughout the challenges of 2020.”
The performance, titled Looking A Lot Like Christmas, will be streamed for free on Donmar Warehouse’s YouTube channel on the evening of 16th December.
Audience members will be encouraged to donate money to support the theatre’s work, with 15% of all money raised going to the Connection at St Martin-in-the-Fields’s homeless charity.
More performers will be revealed in the coming weeks