Ioan Campeanu, 44, plunged the blade into 28-year-old Andra Hilitanu's neck and waited two hours to raise the alarm on June 1 last year.
He drove around central London past Buckingham Palace before returning to his flat in north-west London and calling 999, the Old Bailey heard.
The court was told Ms Hilitanu's 40 stab injuries were all "survivable" and it was possible it could have taken more than 20 minutes for her to die.
Campeanu was found guilty of murdering his seven-month pregnant girlfriend and the destruction of their unborn daughter.
He was jailed for life with a minimum term of 26 years with 14 years for the death of the child to run concurrently.
Sentencing, Mr Justice Jacobs said mother-of-two Ms Hilitanu suffered a "horrible" death, alone and far from her home country.
She suffered 40 stab wounds, including four to the neck, as well as other blunt force injuries during the attack in her Neasden flat, over 25 minutes.
The senior judge rejected Campeanu's claim that his victim had inflicted wounds on her pelvis herself because she did not want her baby.
He told Campeanu: "This was a prolonged and brutal attack in which you showed her no mercy.
"The terror and agony which she must have suffered are awful to contemplate."
Earlier in mitigation, Michael Bromley-Martin QC said: "I described this as a horror case and a lesson perhaps in the dreadful end of the inevitable spiral caused by addiction to drugs and in particular to cocaine."
He said the defendant was in such as state after stabbing his girlfriend that he "had it in his mind to visit Buckingham Palace to ask the Queen for medical assistance".
Prosecutor Brian O'Neill QC said "self-induced intoxication" was no mitigation and pointed out Campeanu had denied any mental health problems when he was seen by two social workers the day before the killing.
The trial had heard the killing came after years of domestic violence at the hands of the defendant, who was brought up in a "brutal" Romanian orphanage.
He had previous convictions in Romania and England for robbery, theft and criminal damage, using crime to finance his drug addiction.
The court was told Miss Hilitanu's cousin had previously seen Campeanu kick her in the groin, saying: "I'll kill you Andra, I'll eat your flesh."
When he finally called 999 to report the fatal stabbing, Campeanu had said: "She's dead, I killed her."
Ms Hilitanu was one of four siblings who were brought close together following the death of their parents early in life.
Her older sister Ramona Hilitanu said in a victim impact statement that Andra's "future was taken away in a cruel manner".
She said: "I do not hate Ioan Campeanu. I am not a hateful person. I am sad at what he has done.
"I am also frustrated at the way in which he left Andra to die. Ioan Campeanu could have sought help from so many sources and yet chose to do nothing. I will never be able to forget this fact."
Detective Inspector Jamie Stevenson, of Scotland Yard, said: "This was Campeanu's final act of brutality against Andra after months and years of domestic violence.
"Despite initially admitting his guilt to the attending officers, Campeanu has since refused to take responsibility for his despicable actions.
"He has unnecessarily put Andra's family through even more pain and suffering by forcing them to re-live Andra's murder at trial.
"My heart goes out to Andra's friends and family and I hope today's sentencing gives them at least a small measure of comfort and closure.
"We will never know if reporting the abuse she suffered could have saved Andra, but I would implore anyone who is suffering or knows of someone suffering domestic abuse to call police immediately."