The newlyweds, who tied the knot just two weeks ago, met each leader attending the summit one by one on a beachfront board walk on Friday afternoon.
Mr Johnson evidently had to remind himself not to shake hands with fellow leaders, repeating the word “elbows” as he met Joe Biden, Angela Merkel, Justin Trudeau, Mario Draghi, Emanuel Macron, Japan’s Prime Minister Yoshihide Suga.
He also met President of the European Council Charles Michel and President of the European Commission Ursula von der Leyen.
Mr Biden was accompanied by wife Jill, while Germany’s Ms Merkel was with her husband Joachim Sauer, with Mr Macron attending with wife Brigitte.
Mr Trudeau of Canada and Mr Draghi of Italy arrived alone.
The group posed for a socially distanced “family photograph” to kick off the G7 summit.
As the group assembled, Mr Biden quipped that “everyone [should get] in the water.”
It is the first face-to-face meeting for the group in almost two years as a result of the pandemic.
The Prime Minister said ahead of the meeting “the world will look to the G7 to apply our shared values and diplomatic might to the challenge of defeating the pandemic and leading the global recovery”.
The politicians will spend the day discussing issues including the pandemic before a lavish reception at the Eden Project attended by the Queen.
William and Kate will also join the Queen, the Prince of Wales and the Duchess of Cornwall at the G7 leaders reception on Friday evening.
The duchess and US First Lady Jill Biden visited an academy school for four to 11-year-olds to highlight the issue of the early years development of children.
Asked by a broadcast journalist if she had any wishes for Lilibet, Kate said: “I wish her all the very best. I can’t wait to meet her.
“We haven’t met yet. I hope that will be soon.”
The leaders are under pressure to do more to share the burden of protecting the world from the virus.
Mr Biden has already promised to donate half a billion Pfizer vaccines for 92 low and lower-middle income countries and the African Union.
Under the Prime Minister’s plan, the UK will provide five million doses by the end of September, with 25 million more by the end of 2021.