Claudia's Law - otherwise known as the Guardianship (Missing Persons) Act 2017 - has come into force.
It means families of missing loved ones will be able to take control of their financial affairs after they have been gone for 90 days or longer.
Chef Claudia Lawrence vanished without a trace from her home town of York 10 years ago and police believe she was murdered.
Her father Peter Lawrence campaigned tirelessly to take hold of his daughter's financial and practical affairs and pushed for a change in law that would make it easier for other families.
Previously, families could only take over the financial affairs of a missing person if they were declared dead under the Presumption of Death Act 2013.
Mr Lawrence, who received an OBE in 2018 for his work with the families of missing people said it was an important change.
"When people are at their lowest emotional ebb they suddenly feel they can't deal with financial and practical things, well now that's over. There are several hundred families queuing up waiting to deal with this. It's really important and thank god it's here," he said.
"Claudia is still missing and we don't know what happened to her. It is distressing and let's hope for everyone else's sake that they are able to deal with their family's affairs."
Applicants will have to satisfy certain conditions including providing evidence to show the person has not been seen for 90 days and a witness statement.
A Ministry of Justice spokesperson said: “Coping with the tragedy of a loved one going missing can cause immense pain and stress.
“Claudia’s Law, campaigned for so tirelessly by Peter Lawrence, will mean that from today families can manage their loved one’s affairs in their absence – removing an enormous burden at such a distressing time.”
The Guardianship (Missing Persons) Act 2017 Code of Practice has more detailed information and the MoJ said it will publish a step-by-step guide on gov.uk.