The 69-year-old League-Nawaz (PML-N) supremo agreed on Friday to go to the UK for the treatment, heeding doctors' advice and accepting his family's request.
"Nawaz Sharif is leaving for London on a Pakistan International Airlines flight on Sunday morning along with his brother Shahbaz Sharif for his treatment," a senior party leader told PTI.
Although his name is in the no fly-list, the Imran Khan government has assured to remove it by Friday evening, he said.
Sharif is leaving for London after doctors categorically told him that they had exhausted all the options available in Pakistan and seeking treatment abroad was the only one left, the leader said.
The three-time premier has already secured bail in Al-Azizia Mills corruption case for eight weeks on medical grounds and in the money laundering case. In Al-Azizia case, Sharif was serving a seven-year imprisonment in Lahore's Kot Lakhpat jail.
His daughter Maryam Nawaz will not accompany him as she had to surrender her passport to the Lahore High Court as a surety against the bail granted to her in the money laundering case. She may explore the option of going to London later, the PML-N lader said.
According to him, Sharif's sons -- Hasan and Hussain -- and another daughter Asma, who live in London, will look after him.
On Saturday, Sharif's platelet count was over 20,000.
"As his platelet count should be 50,000 and beyond for travel abroad, the doctors may give him high dose to increase his platelets, enabling him to undertake the travel," he added.
The Pakistan government decided to let Sharif go abroad for treatment due to his critical medical conditions.
Arrangements have been made for Sharif's treatment at Harley Street Clinic.
Sharif's family have contacted two doctors in London. An appointment has been made at the Harley Street Clinic for Monday. The Sharif family are also talking to a doctor in New York, Geo News reported.
Shehbaz has already spoken to consultants at one of the Harley Street clinics where patients suffering form drop in platelets are treated privately, the report said.
Earlier Speaking to the media on Friday, Sharif's daughter Maryam, 46, said the family could not risk Sharif's health and has decided to send him abroad.
"Shehbaz Sharif is looking after all the boarding and lodging of the former premier. After losing my mother last year, my father is my everything now," a distraught Maryam told the ARY News.
Sharif's wife Kulsoom died of throat cancer in London last year.
In Islamabad, Prime Minister's Special Assistant Naeemul Haq said on Friday the "government has no issue if he (Sharif) flies abroad for treatment".
Khan said that allowing Sharif to go out for treatment was not a concession as he would have to face the charges after recovering.
Sharif's medical reports were sent to doctors in London earlier and they have advised him to come to London for treatment as soon as possible.
However, Minster for Aviation Ghulam Sarwar alleged that Sharif's medical reports were manipulated to show him critically ill so that he could be allowed to leave the country.
"He (Sharif) has once again made a deal with the government like he did in 2000 (with the Pervez Musharraf government) to go out of the country," Sarwar alleged.
Sharif was arrested by Musharraf after toppling his government in 1999 but allowed him to go on exile to Saudi Arabia.
PML-N spokeswoman Marryium Aurangzeb called Sarwar's statement as "callous" and by someone who had no heart for an ailing person.
Sharif was lodged in the Kot Lakhpat jail but last month he was sent to the custody of the National Accountability Bureau (NAB) which is probing the Sharif family in the Chaudhry Sugar Mills corruption case.
On December 24, 2018, an accountability court had sentenced Sharif to seven years in prison in the Al-Azizia Steel Mills corruption case and acquitted him in the Flagship case.
On October 25, the Lahore High Court granted bail to Sharif in the Chaudhry Sugar Mills case. He was undergoing treatment after being diagnosed with an acute immune disorder.
On October 29, the Islamabad High Court suspended Sharif's sentence in the Al-Azizia corruption case for eight weeks on medical grounds.
The Sharif family has denied all corruption charges and termed them as politically motivated.