The King and Queen will attend the Easter Sunday service at St George's Chapel at Windsor Castle, Buckingham Palace has confirmed.
This will be one of the most significant events King Charles will have attended since his cancer diagnosis last month.
The King and Queen will be joined at the service by other senior royals.
But the Prince and Princess of Wales will not be there, as Catherine continues with her cancer treatment.
The announcement that the King, aged 75, will be at the Easter morning church service will be seen as an encouraging sign about his health.
He has continued to carry out meetings and kept up his work as head of state. But he has not been at public events this year, after having treatment for an enlarged prostate and later revealing that he had been diagnosed with a form of cancer.
The King will be with Queen Camilla, who has been carrying a number of solo royal engagements in her husband's absence.
The Princess of Wales, who put out a video statement last week about being treated for cancer, is continuing her recovery. It had already been announced that she would not be at the Easter service at the church on the Windsor estate.
Her husband Prince William and their three children will also not be at St George's Chapel on Sunday.
There have been calls for her privacy and she will be spending more time out of public sight as she receives treatment.
The Easter church service is a regular feature of the royal calendar, usually attended by many senior royals, but this year it is expected to be a smaller gathering.
In the run-up to Easter, King Charles hosted a gathering of faith leaders in Buckingham Palace.
The meeting on Tuesday was in support of a charity that brings together representatives of religious faiths, including Christian, Muslim and Jewish leaders.
Building bridges between religions and encouraging tolerance has been a long-standing cause for King Charles.
