The presentation to Daithi Mac Gavan was one of the Prime Minister's official duties to coincide with US President Joe Biden's visit to Northern Ireland.
Northern Ireland's new organ donation law has been named after the Belfast boy, to honour his and his family's campaign for legal change.
Mr Sunak is due to meet Mr Daithi and his family as part of the Chancellor's daily Points of Light awards.
The No. 10 Minister said he thanked Mac Gavan for his “tireless campaigning” for the passage of the Daity Bill, which introduced an opt-out organ donation system and brought Northern Ireland on par with the rest of the UK.
Their efforts led to the Northern Ireland Minister's decision earlier this year to introduce amendments to the Executive Organisation Bill, allowing Daithi's Law to “become a reality and save lives across Northern Ireland”, No. 10 said.
From June, all adults in the region will be considered potential organ donors, unless they refuse or belong to an excluded group.
Those excluded from the deemed consent law are children under 18, people who lack the mental capacity to understand changes to the law, visitors to Northern Ireland and temporary residents.
In a letter to Daithi, who is waiting for a new heart transplant, Mr Sunak said: “Every day I write a letter to thank someone who has done something wonderful for someone else. Today is very special because I can thank you.”
“The courage and determination you have all shown in campaigning to change the law on organ donation in Northern Ireland is truly inspiring.
“With Daithi's Law, you're helping other people in the same situation as you get life-changing help, which is a huge accomplishment.”
“Your father used to say, 'Extraordinary things happen to extraordinary people.'”
“I agree with him that you are truly an extraordinary person, so I am delighted to honour your bravery by nominating you as the UK’s 2,029th Point of Light.
“The whole country is rooting for you as you continue your treatment.”
Sunak will host his third meeting with President Biden since taking office, during which they will discuss the broad and deep relationship between the UK and the US, epitomised by joint UK and US investment in Northern Ireland's economy and people.
The Prime Minister is expected to use President Biden's visit and meetings with Belfast business leaders to encourage further long-term investment.
Events marking the anniversary of the Good Friday Agreement will continue next week, with the Prime Minister visiting Belfast again to address an “Agreement 25” conference at Queen's University and host a special gala dinner to mark the anniversary.
