Opt-out organ donation will become law from 2020 after a Government bill was finally approved today.
The Queen has given royal assent for the bill, also known as Max and Keira's law after the donated heart of Keira Bell, nine, saved the life of Max Johnson, 10, in 2017.
This means The Organ Donation Act's changes to consent will come into effect next year.
Expected to save hundreds of lives every year, the change will mean all adults' organs can be taken after they die unless they specifically tell the NHS otherwise.
Schoolboy Max Johnson said: 'Even if it saves just one life, it will be worth it.'
Max and Keira's Law, named after a boy who received a heart transplant from a girl who donated it, cleared the House of Commons last year. Max Johnson (left) was saved by a heart given to him by the family of nine-year-old donor Keira Ball (right) following her death in 2017
Prime Minister Theresa May has praised the bill, saying: 'I'm delighted Max and Keira's law has passed today.
'It marks a momentous step for thousands of people in need of a life-saving transplant, and could save as many as 700 lives a year.'
There are currently more than 6,000 people on the organ donation waiting list in the UK – last year at least 400 people died before a suitable donor could be found.
Only around one per cent of people's organs are useable after they die.
They must be used quickly and still in suitable condition, and the NHS Blood and Transplant service says intensive care patients tend to be the only ones who can donate.
Mrs May added: 'With significantly more people willing to consider organ donation than are actually registered as donors, this vital step will presume consent unless people choose to opt out of being a donor.
'It's important that everyone takes the time to discuss their choices on donation with their families and register their wishes, whatever their preference may be.
'I also want to thank those who have campaigned tirelessly to raise awareness of this issue, and pay particular tribute to Max, Keira and their families for making this historic change happen.'
Research has found some 80 per cent of people in the UK support the concept of organ donation after death but only 38 per cent of adults have actually signed up.
The law change began last year and passed through the House of Commons and House of Lords with ease.
This left only Royal Assent – the