The Duke of Sussex will return to the UK in just over a week for a ceremony marking the 10th anniversary of the Invictus Games.
Prince Harry is expected to attend the thanksgiving service at St Paul's Cathedral, London, on 8 May.
The prince will give a reading during the service, while actor Damian Lewis will recite a poem.
Prince Harry was last seen in the UK in February for a brief visit to see King Charles after his cancer diagnosis.
It is the first major event he will have attended in Britain for some time.
The prince launched the Invictus Games, a sport event for military personnel wounded in action, in 2017.
The ceremony will mark "a decade of changing lives and saving lives through sport," a spokesperson for the Games said.
The duke moved to the US with his wife, Meghan, Duchess of Sussex, after they stepped back as senior royals in 2020.
The spokesperson did not say whether the prince will be joined by Meghan for the ceremony.
In an interview in February with ABC News, Harry said he "jumped on a plane" as soon as possible to see King Charles after the cancer diagnosis - and was "grateful" for the time spent together.
He also suggested there would be more visits to the UK, saying: "I'll stop in and see my family as much as I can."
The upcoming visit comes as Buckingham Palace confirmed King Charles, 75, will resume public engagements next week after making encouraging progress in his cancer treatment.
The King will begin with a symbolic trip to a cancer treatment centre next Tuesday, while his summer plans include a state visit, where he will host the Emperor and Empress of Japan.
"It is too early to say" for how much longer his treatment will continue, the palace said.
It added that doctors were "very encouraged by the progress made so far and remain positive about the King's continued recovery".
The type of cancer has not been disclosed, but the King's medical team are "sufficiently pleased with the progress made so far that the King is now able to resume a number of public-facing duties".
It has been a difficult start to the year for the Royal Family, with the Princess of Wales also undergoing treatment for cancer.
In a statement released in March, Catherine said the diagnosis was a "huge shock" after an "incredibly tough couple of months".
She said the cancer was discovered after she had abdominal surgery in January, saying tests after the operation "found cancer had been present".
"My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment," she said.
Details of her cancer have not been disclosed, but Kensington Palace said it was confident the princess would make a full recovery.
The princess said she was thinking of all those who have been affected by cancer, adding: "For everyone facing this disease, in whatever form, please do not lose faith or hope. You are not alone."
The King was said to be "so proud of Catherine for her courage" in speaking about her treatment.
He has been in the "closest contact with his beloved daughter-in-law", the palace said.
