The House of Windsor made the update Monday, putting Lilibet at eighth in line for the throne. She was born June 4.
Harry and Markle left royal life to live independently in California. In an interview with Oprah Winfrey earlier this year, Harry said the move was partially due to racism in England. Markle is bi-racial.
Markle, an actress, has said she had suicidal thoughts due to the stress of being a member of the royal family.
She won a privacy lawsuit against a British tabloid earlier this year after it described her estrangement from her father.
A film based on the couple's official break-up with the royal family was recently released.
Last week, Harry announced a forthcoming memoir.