The event will be just one of a handful of appearances that Prince William's wife has made since she was diagnosed with cancer in March, underscoring the importance of the gas-rich gulf state of Qatar that invests billions in the UK and has played a central role in ceasefire talks between Israel and Hamas.
William and Kate greeted Sheikh Tamim bin Hamad Al Thani and Sheikha Jawaher bint Hamad bin Suhaim Al Thani in the morning.
The royal family has welcomed the Qatari emir and his wife to the United Kingdom. (AP PHOTO)
The couples then travelled to Horse Guards Parade in central London, where King Charles formally welcomed the emir and Sheikha Jawaher to the UK at the start of a two-day visit that will include a trip to Westminster Abbey, a banquet at Buckingham Palace and a meeting with Prime Minister Keir Starmer.
Queen Camilla, who has been suffering from a lingering chest infection, pulled out of the formal outdoors event on medical advice.
She plans to take part in a lunch at the palace and attend the evening banquet.
Although being smaller than Tasmania, Qatar has the world's third-largest reserves of natural gas and is a key investor in the UK.
The Qatari Investment Authority owns the luxury retailer Harrod's and holds large stakes in companies such as Barclays Bank and the supermarket chain Sainsbury's.
It has also invested heavily in London real estate including the Shard, western Europe's tallest building.
But the display of pomp being rolled out for the emir sits uneasily with human rights advocates who say women and LGBTQ people face discrimination in Qatar, and migrant workers still have not been compensated for "egregious abuses" that occurred during preparations for the 2022 football World Cup.
"Hosting the royal visit without addressing these issues is tantamount to royal-washing Qatar's troubling rights record," said Yasmine Ahmed, UK director of Human Rights Watch.
The state visit comes at the end of a difficult year for the royal family.
The King was sidelined for two months after it was announced in February that he had been diagnosed with an undisclosed form of cancer.
Just a few weeks later, Kate made public her own cancer diagnosis and said that she too would be stepping away from public duties to focus on her treatment and recovery.
While Charles returned to public duties at the end of April, Kate needed more time and her return has been slower.
The princess has made only a few public appearances this year.
They included the King's annual birthday parade in June and the men's final at Wimbledon in July.
Most recently, she took part in the annual Remembrance Day ceremonies in November to honour the country's war dead.
The princess announced in September that she had completed chemotherapy treatment.
One reason the government and royal family may have asked Kate and William to play a major role in the Qatari state visit is because they have a lot in common with the emir.
All three are in their early 40s and were educated at elite British prep schools.
The emir and William are both graduates of the Royal Military Academy at Sandhurst, with the emir going on to serve in the Qatari military and William serving in both the British Army and Royal Air Force.
Kate and William will join the Qatari royals and the King and Queen for a carriage procession to Buckingham Palace.
After lunch at the palace, the emir and Sheikha Jawaher will visit Westminster Abbey and the Houses of Parliament.
Later in the day, the King and Queen will host a state banquet at Buckingham Palace.
17°C