Father-of-four Michael McGibbon, 33, was shot three times in the legs in an alleyway in a nationalist area of north Belfast on Friday, 24 hours after two men threatened him at his house.
Northern Ireland Secretary Ms Villiers condemned those who believe it is acceptable to take the law into their own hands and “administer this violent, brutal treatment” of people such as Mr McGibbon.
She offered her thoughts to Mr McGibbon’s family and praised his widow Joanne as an “incredibly brave” woman.
Speaking in the Commons, shadow Northern Ireland secretary Vernon Coaker said Mr McGibbon’s death was one of two “terrible” shootings in recent days.
He said: “The PSNI says that the attacks have all the hallmarks of paramilitary assaults, so on the streets of this United Kingdom we have shootings and murders linked to paramilitary activity. It is both sickening and totally unacceptable.
“Will you tell us more about what happened and what action you, the PSNI and others will take against those who have no respect for human life or the rule of law?”
Ms Villiers replied: “You choose your words correctly - this is absolutely sickening.
“I feel that this case could be like a number we have seen over recent decades in Northern Ireland and be the point at which people there say that this is completely and utterly unacceptable.
“The police investigation is progressing, with an individual charged with murder, but it is also imperative, as (Democratic Unionist MP Nigel Dodds) said, that we implement the Fresh Start agreement proposals, including progress on the strategy that the panel is coming up with.
“We need to ensure that people have the confidence to come forward and give evidence against these individuals.”
Earlier, Mr Dodds (Belfast North) said the “brutal slaying” of Mr McGibbon was an “atrocious” event.
He asked Ms Villiers: “Will you join me in commending the courageous words of Mr McGibbon’s widow who has called for people to stand together against these paramilitary terrorists who carried out this atrocious attack?
“Do you agree that it is vital that we all unite against terrorists from all sides and that we get on with implementing the provisions to tackle paramilitaries in the Fresh Start agreement?”
Ms Villiers agreed with Mr Dodds, adding: “Mr McGibbon’s widow is an incredibly brave woman. The circumstances of Mr McGibbon’s death are deeply tragic and heartbreaking.
“I know that the whole House will feel for his family at this time and it is utterly unacceptable that, in modern Northern Ireland, there are still people who believe that they can take the law into their own hands and administer this violent, brutal treatment of individuals such as Mr McGibbon. It is utterly unacceptable.
“I agree with you that everyone in Northern Ireland should join the widow in this case and condemn that horrific and brutal murder.”