Millions of people around the world are set to tune in to watch Prince Harry and Meghan carry out their final public engagement before they step back from being senior royals. 

The couple will be embarking on a new chapter in North America, but first, they will join the Queen, Prince Charles and his wife Camilla at the annual Commonwealth Day service at Westminster Abbey in London next week.

Since shunning the spotlight on the royal family with their decision to quit royal life in January, the Duke and Duchess of Sussex are yet to be seen publicly with their royal counterparts, further highlighting the significance of the event. 

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Meghan and Harry wishing Welsh followers a Happy St Davids Day on March 3. Photo: Instagram

Also present at the service on March 9 will be Prince William and Kate Middleton in what will be Harry and Meghan's last appearance as senior royals.

Royal fans everywhere will have full viewing pleasure as the service is scheduled to be broadcast live on BBC One and across the BBC World Service.

International boxing champion and Olympic gold medallist Anthony Joshua will deliver a reflection, while singers Alexandra Burke and Craig David will perform.

Apart from being physically present, the royal family's main job will be to greet those involved in the service and walk past the Commonwealth flag bearers as they leave.

That will be Harry and Meghan's final royal duty before stepping away from the monarchy completely and into a dual role, supporting the Queen, enabling them to live a life mostly in North America, from March 31.

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The Duke and Duchess of Cambridge with Harry and Meghan at 2019's Commonwealth Day service. Photo: Getty

Guests of honour among the 2000-strong congregation will include British Prime Minister Boris Johnson, the Commonwealth secretary-general Baroness Scotland, high commissioners, ambassadors, faith leaders and more than 800 schoolchildren and young people.

Tradition dictates that sixth-in-line Harry sits with Meghan in the second row of seats behind the Queen, Charles, Camilla, William and Kate during the service.

The Queen and the royal family will meet people involved in the service and walk past the Commonwealth flag bearers as they leave.

Prince Andrew will be absent this year, having stepped down from public life following a disastrous television interview over his friendship with convicted sex offender Jeffrey Epstein.

-with AAP