The law was narrowly approved by the Dutch Senate on Tuesday in a 38-36 vote. It passed the lower house of Parliament in 2016 by a slim 75-74 margin.
The law is expected to be implemented in 2020 after approval from King Willem-Alexander.
The new policy is meant to help fix a shortage in organ donations in the Netherlands, according to its drafter, Pia Dijkstra, a member of the House of Representatives.
Every person over 18 who is not registered will receive a letter asking whether they wish to donate their organs. Failure to respond to this letter -- or another six weeks later -- will result in that person being considered a donor by default.
"They will be able to reply: yes, no, my next of kin will decide or a specific person will decide," Djikstra said in a statement.
Anyone can change their organ donation status at any time, according to the bill.
There are about 1,100 people waiting for organ donation in the Netherlands, according to Jeantine Reiger, communications manager for the Dutch Transplant Foundation
The law is also meant to put less pressure on family members to decide the fate of their loved one's organs, she said.
"When no registration about the donatee is available, the bereaved have to decide on donation of the organs," Reiger said. "That is very difficult for them. They are emotionally shaken by the sudden death of their family member."
Similar laws are in place in Belgium and Spain, where the policy is referred to as "presumed consent."
But it is not always enforced in Spain, according to Anne Paschke, public relations manager for the United States nonprofit United Network for Organ Sharing.
"They have a soft opt-out system where they will not recover (organs) if the family objects," she said. "So even though it's opt-out, it's not like a hard opt-out, where they would recover anyway."
In the Netherlands, support for the policy appeared to drop after the bill passed the lower house of Parliament in 2016. During a Donor Week event in October 2016, a month after that vote, 26,430 adults registered as non-donors, but only 5,414 people registered as donors, according to the Ministry of Public Health
Over 11,000 residents changed their status from donors to non-donors during the Donor Week.
In the United States, where would-be donors must opt in or explicitly consent, organ donations have been increasing. In 2017, more than 10,000 people became deceased donors -- the fifth consecutive record year, according to the United Network for Organ Sharing
"Polling shows that more than 90% of people in the United States are in favor of organ donation," Paschke said. "A little over 50% are actually signed up in the donor registry."
But "presumed consent" is unlikely to take hold in the United States, according to Paschke.
"Laws would have to change in every state, and the people that it would appeal to are people who are already donation supporters," she said. "But there are people who aren't ready to make a decision, and if you force them to make a decision, it could have some unintended consequences."
There are 114,989 candidates on organ transplant waiting lists in the United States, according to the US Department of Health and Human Services
. Over 80% are waiting for a kidney, 12% for a liver and 3% for a heart.
"The good news is that we had a record number of deceased donors and transplants last year. About 95 people a day got a transplant," Paschke added. "But that's not enough. About 20 people die waiting for an organ that doesn't come in time."