The law change marks the end of a two-year campaign by Lissie Harper after her husband, police officer Andrew Harper, was killed in the line of duty while answering a late-night burglary call.
Mrs Harper, 30, previously said she was “outraged” over the sentences handed to the three teenagers responsible for her husband’s death.
The so-called Harper’s Law is expected to make it on to the statute books in an amendment to the existing Police, Crime, Sentencing and Courts Bill, meaning it is likely to get Royal Assent and become law early next year.
Mrs Harper said: “It’s been a long journey and a lot of hard work. I know Andrew would be proud to see Harper’s Law reach this important milestone.”
Pc Harper, 28, died from his injuries when he was caught in a strap attached to the back of a car and dragged down a winding country road as the trio fled the scene of a quad bike theft in Sulhamstead, Berkshire, on the night of August 15 2019.
Henry Long, 19, was sentenced to 16 years and 18-year-olds Jessie Cole and Albert Bowers were handed 13 years in custody over the manslaughter of the Thames Valley Police traffic officer.
Long, the leader of the group, admitted manslaughter, while passengers Cole and Bowers were convicted of manslaughter after a trial at the Old Bailey.
All three were cleared of murder by the jury.
The sentences prompted Mrs Harper to lobby the Government to better protect emergency services workers on the front line.
Announcing the intended law change, Justice Secretary Dominic Raab said: “We are going to pass into law mandatory life sentences for those who unlawfully kill an emergency worker in the course of their duty.
“I pay tribute to Lissie Harper’s remarkable campaign.
“This Government is on the side of victims and their families and we want our emergency services to know that we’ll always have their back.”
Mr Raab said the law will not be retrospective, meaning Pc Harper’s killers cannot have their sentences extended. The Court of Appeal previously rejected a bid by the Attorney General to increase their sentences.
The Police, Crime, Sentencing and Courts Bill is currently being considered in the House of Lords and both peers and MPs would have to agree to the proposed amendment to introduce the new law as part of the legislation.
Home Secretary Priti Patel, said: “Pc Andrew Harper’s killing was shocking.
“Those who seek to harm our emergency service workers represent the very worst of humanity and it is right that future killers be stripped of the freedom to walk our streets with a life sentence.”
Mrs Harper said: “Emergency services workers require extra protection.
“I know all too well how they are put at risk and into the depths of danger on a regular basis on behalf of society.
“That protection is what Harper’s Law will provide and I am delighted that it will soon become a reality.”