An Indonesian woman was jailed for 20 years Thursday for murdering a friend from an Australian college with poisoned coffee in a "sadistic" fashion, capping a sensational trial that has gripped the country.

Jessica Kumala Wongso, 28, who is also an Australian permanent resident, was found guilty of murdering Wayan Mirna Salihin by slipping cyanide into her drink at an upmarket Jakarta cafe, sparking applause from spectators in the packed courtroom.

The soap opera-style tale of two members of Indonesia's wealthy elite having a dramatic fallout that culminated in murder has captivated the country, with the trial dubbed the "poisoned coffee" case and broadcast live on national TV for months.

The murder, which Wongso carried out in January after becoming angered at 27-year-old Salihin's criticism of her boyfriend, also generated huge interest in Australia, where the women studied together at a Sydney design college.

After hours reading the verdict in a courtroom overflowing with hundreds of journalists and members of the public, a three-judge panel declared Wongso guilty of premeditated murder and handed down the lengthy jail sentence.

"The defendant's action was deplorable and sadistic because it was committed against her own friend," presiding judge Kisworo, who like many Indonesians goes by one name, told the court.

"The defendant did not regret her action and claimed she did not do it."

Wongso, who denies carrying out the crime, was emotionless as the ruling was handed down, then told the court: "I cannot accept the verdict, it's very unfair."

Her legal team said they would file an appeal.

- Sobs of relief -
Some of Salihin's relatives sobbed with relief after the verdict, with her twin sister Sandy telling journalists: "This is very hard, I am grateful."

The victim's supporters had rallied outside court throughout the day waving signs that read "Justice for Mirna", and when the hearing concluded gave out white roses to police and journalists.

After drinking the iced Vietnamese coffee at the cafe in one of Jakarta's fanciest malls, Salihin collapsed and began convulsing, then died soon afterwards in hospital.

Prosecutors said Wongso decided to murder Salihin after she advised the defendant to break up with a boyfriend as he was using drugs, saying that the "cruel" crime was planned "meticulously".

Police say that she placed bags on the table to prevent CCTV cameras in the cafe from filming her slipping the poison into the coffee.

Wongso had vehemently denied murdering her friend, breaking down in tears as she took the stand during the trial to reject the allegations.

She had testified that she could not remember key details about the day and her defence team asserted the case against their client was weak and lacked evidence to prove guilt.

During the months-long trial, which began in June, three forensic experts called by the defence testified there was no proof Salihin's death was caused by cyanide poisoning.

Australian authorities assisted with the case after receiving assurances that Wongso would not be handed the death penalty if found guilty of murder, a capital crime in Indonesia.