"Wishing Archie a very happy first birthday today!" the couple wrote on their Kensington Royal account.
Harry and the former Meghan Markle also released a new video filmed by Harry that shows Meghan reading to their son to mark the special day.
Archie's big day follows the recent birthdays of his cousins, Prince Louis and Princess Charlotte, who are with the royal family at their home in London while Archie celebrates with his parents at their new home in Los Angeles.
William and the former Kate Middleton were most recently together in public with Harry and Meghan in March, when the Duke and Duchess of Sussex made their final official appearance as senior members of the royal family at the Commonwealth Day service at Westminster Abbey in London.
Meghan greeted Catherine, Duchess of Cambridge, briefly at the event, while the brothers maintained a seemingly icy distance after barely exchanging a few words during the ceremony.
It was a contrast to happier times like last summer when baby Archie joined his cousins for his first public family outing as they cheered on Harry and William during a charity polo match.