Top Western and Ukrainian officials as well as international organizations such as the European Council and the European Parliament have appealed for over a year for Russia to free Nadezhda Savchenko.
German Chancellor Angela Merkel is reported to have spoken directly to Russian President Vladimir Putin about her case - to no avail.
On Thursday, the Ukrainian military pilot's trial in the small southern Russian city of Donetsk, not far from the Ukrainian border.
Preliminary hearings will be held behind closed doors, marking the beginning of one of the most controversial trials in Russia in recent years.
Savchenko is among more than a dozen Ukrainian prisoners who the Ukrainian Foreign Ministry said are being held in Russia "for political reasons."
The Russian human rights organization Memorial has classed Savchenko as a "political prisoner" and demanded her release.
Initially, Russian officials accused the 34-year-old of being an accessory to murder during the conflict in eastern Ukraine.
But, a few months before the start of the trial, the charges against her were changed to include murder.
She is also being charged with illegally crossing the border into Russia.
If convicted, her lawyers anticipate a prison sentence of over 10 years, although she could face a maximum sentence of 25 years.
Brought secretly over the border
In the summer of 2014, Savchenko left her post in the Ukrainian army to fight in the Aidar volunteer battalion against separatists in the eastern Ukrainian region of Luhansk.
Russian investigators have accused her of telling the Ukrainian army about the presence of a group of pro-Russian fighters in mid-June.
During the shelling that followed near Luhansk, several people died, including two Russian journalists.
Savchenko now stands accused of their murder.
Savchenko has said she is innocent and has claimed to have been taken prisoner by separatists and secretly smuggled over the border to be held first in a prison in southern Russia before being brought to Moscow.
In Ukraine, Savchenko has been celebrated as a martyr.
In March, Ukrainian President Petro Poroshenko officially named her a "hero of Ukraine."
She is often referred to in the Ukrainian media as the nation's "G.I. Jane."
Savchenko is one of a very few women in the Ukrainian air force.
"Really, she wanted to become a military reporter," her mother, Maria Savchenko, told DW.
But the family did not have enough money for that, so her daughter became a professional soldier instead.
As a helicopter pilot, Savchenko flew missions in Iraq in 2004 and 2005 after Ukraine joined the US-led coalition in the Iraq War.
Aside from appeals from politicians, there have been two attempts to secure Savchenko's release.
In October 2014, she was elected to the Ukrainian parliament in absentia.
Former Prime Minister Yulia Tymoshenko put Savchenko at the top of the list of her All-Ukrainian Union "Fatherland" party.
Critics accused Tymoshenko of using Savchenko's popularity to boost her falling approval ratings.
Tymoshenko's party also nominated Savchenko to be a delegate to the Parliamentary Assembly of the Council of Europe, a move that gave her international immunity.
Russia, though, was unmoved.
Kiev hoping for exchange after verdict
Most recently, Ukraine hoped to secure Savchenko's freedom within the framework of the Minsk Agreement negotiated between Ukraine's government and separatists in February.
That ceasefire deal, which has not been completely observed by either side, provides for the release of all prisoners.
Moscow, however, said no.
But some observers have said they expect Russia to hand down a long sentence to Savchenko, thereby making an example of her.
Such an action has a precedent in Russia, where a court in 2012 sentenced members of the punk band Pussy Riot to two years for hooliganism.
Russian businessman and opposition activist Mikhail Khodorkovsky was also only released in 2013 after serving 10 years of his sentence for fraud.
Ukrainian officials hope Russia will pardon Savchenko and release her after the court issues its verdict.
Russian Foreign Minister Sergey Lavrov hinted at that possibility in April.
In Kiev, there is also speculation that she might be offered in exchange for two Russian officers taken prisoner in eastern Ukraine who are now being held and awaiting trial in Kiev.
Source: Deutsche Welle