The father of Clare Wood, who died at the hands of a violent ex-boyfriend, said he was "quietly elated that common sense has come to the fore" after the introduction of what has become known as Clare's Law.
"I'm glad it escalated into what it has become," Michael Wood said.
Today's national roll-out of 'Clare's Law' has been chose by the Home Secretary as it also coincided with International Women's Day and the launch of Domestic Violence Protection Orders.
DVPOs will enable police and magistrates' courts to provide protection to victims in the immediate aftermath of a domestic violence incident.
Mrs May said: "Domestic abuse shatters lives and this Government is working hard to provide police and local authorities with the tools they need to keep women and girls safe.
"Clare's Law and DVPOs are just two of a raft of measures we have introduced to hand control back to the victim by ensuring they can make informed decisions about their relationship and escape if necessary.
"Protection for victims is improving but sadly there are still too many cases where vulnerable people are let down."
A father whose daughter was murdered by an ex-boyfriend with a secret violent past today said he was "absolutely delighted" women across the country have today been given the "right to know" their partner's history.
The scheme, known as Clare's Law is named after Clare Wood, 36, who was strangled and set on fire by her ex-boyfriend George Appleton at her home in Salford, Greater Manchester.
Clare's Law gives women for the first time the right to know if a partner has a history of domestic violence and is being rolled out to police forces across England and Wales following a successful pilot scheme.
Clare Wood's father, Michael Brown, a retired prison officer from Batley, West Yorkshire, who spearheaded the "right to know" campaign after his daughter's murder in 2009, said today: "I'm absolutely delighted."
"I must admit it's tinged with a bit of emotion and a bit of sadness but we have got what we were fighting for - to bring protection into the country for half the population."
Step One: Initial contact - police take details on what prompted an enquiry and the nature of a relationship before running initial checks and a risk assessment.
Step Two: Face to face meeting - to gather more information. Police may run checks with other agencies including the prison service, the probation and social services.
Step Three: Multi agency meeting - police meet other safeguarding agencies (such as the probation service, prison service, social services). They decide whether disclosure is lawful, necessary and proportionate to protect a person.
Step four: Potential disclosure - if checks show a record for abusive offences or disclosure would prevent further crime, the police may disclose information to protect a potential victim.
Theresa May has said Clare's Law will provide people with the information they need to escape abusive situations before it "ends in tragedy".
The pilot scheme, named after Clare Wood who was strangled and set on fire by her boyfriend, will allow women to check police records to see if a partner has a violent background.
The Home Secretary revealed that 88 women were killed by a violent partner or ex-partner last year, and said there was "considerable confusion" about when or if police can share information on someone's violent past with the public.
"Domestic abuse shatters lives - Clare's Law provides people with the information they need to escape an abusive situation before it ends in tragedy," she told The Sun.
"The national scheme will ensure that more people can make informed decisions about their relationship and escape if necessary. This is an important step towards ensuring we do better by women like Clare Wood in the future."