Megan Markle will make her first public appearance after Lilybert was born.
Meghan and her husband, Prince Harry, will be in New York's Central Park at a live global citizenship event this Saturday.
The couple are campaign chairmen of Vax Live: The Concert to Reunite The World, the first vaccine-related event at Sophie Stadium in Los Angeles in May.
Meghan was pregnant at the time and did not appear on stage, but appeared in a video, while Harry was alone at the stadium to call for a stake in the vaccine.
Prince Harry said on stage: "The virus has no borders, and the route to vaccine cannot be determined by geographical location. ”
"It must be accepted as a fundamental right of all, and that is our starting point."
Prince Harry shared the stage with Jennifer Lopez and the Spitfires.
The 24-hour livestream was attended by stars including Australians Hugh Jackman and Keith Urban, as well as Lord, Ed Sheeran, Wicken, Adam Lambert, Blackeye, Green Day and Coldplay.
Several events are taking place around the world, including Lagos, Paris, New York, London, Sydney, Seoul, Rio de Janeiro and Los Angeles.
Prince Harry and Meghan have pushed for vaccine rights several times this year, including an open letter to big pharma urging them to share vaccines with the world's poorest countries.
They also launched a campaign on Archie's birthday in May asking fans to donate to the Gavi Alliance, which raised $4.84 million in the process.
Megan's appearance at the Global Citizen Scene will be her first public appearance in three months since giving birth to her second child.