The carol service is supported by the Royal Foundation, the charity which supports the work of the prince and princess.
It will be attended by members of the Royal Family along with around 1,600 invited guests, among them people who have worked to support others, through their work or by volunteering.
Those being honoured have been nominated by charities associated with the Royal Family or by lord lieutenants, who represent the King in counties around the country.
The event will also hear musical performances from stars including Paloma Faith, Olivia Dean, and Gregory Porter.
It will be broadcast on ITV1 as part of a special programme on Christmas Eve.
Fifteen Together At Christmas services will take place around the country, including at the Royal Cornwall Hospital in Truro and Blackpool Tower Circus.
Kensington Palace said the service would provide “a moment to reflect upon the importance of love and empathy, and how much we need each other, especially in the most difficult times of our lives”.
It said the princess wanted to “celebrate the many people supporting those in need – individuals who have inspired, counselled, comforted, and above all else shown that love is the greatest gift we can receive”.
