Her crime: refusing to say sorry. The judge, aged 34, is the head of Ethiopia's most popular political party, the only female leader of a main opposition party in Africa.
The government in Addis Ababa had her arrested on 28 December, claiming she had violated the terms of an earlier pardon.
Her previous release in 2007, which came after serving two years in prison, was conditional on her signing an apology for taking part in protests against fixed elections.
In November, the woman who is becoming a democratic icon in Ethiopia told an audience in Sweden that she had not asked for a pardon. On returning to Ethiopia it was demanded that she sign further apologies and, when she refused, she was re-arrested. The Ministry of Justice then issued a statement reimposing her life sentence.
Mesfin Woldemariam, an award-winning Ethiopian human rights campaigner, is clear about what she says is going on: "She refuses to bow to them. They want her to submit, but she didn't submit when she was a judge. That's why she left the bar. And she won't now. She's a tough cookie." She won national acclaim by defying government control of the courts and resigning the bar to practice law after high-profile decisions were overturned.
The charges against her go to the heart of Ethiopia's experiment with democracy in 2005 and the violent backlash that followed the country's flawed first attempt at a multi-party election.
When demonstrators, including Ms Mideksa, took to the streets to protest at the skewed results which returned the ruling party, the police opened fire, killing at least 187 people. The opposition leadership, along with thousands of others, were rounded up and jailed.
"In 2005, we expected the results of the national parliamentary elections as a strong foundation for building a temple of democracy in Ethiopia," she told a US Senate hearing in 2007. "Our hopes were dashed, and we found ourselves trapped in a burning house of tyranny."
Her response since being released has been to unite the fragments of opposition into a single party committed to non-violence, democratic reform and an independent judiciary.
A mother who has missed much of her five-year-old daughter's life so far, she has shown remarkable courage. "I'm not afraid of going to jail," she said last year after founding the Unity for Democracy and Justice Party. "Not because that is not a possibility. I know that could happen."
Professor Woldemariam was with her when it did happen. Five cars pulled up and the pair were confronted violently by police while on a street in the capital city. "They behaved as if there was a prize for the first person who got her," the former Fulbright scholar and now professor of geography recalls.
When he asked why they had not issued a warrant and asked her to give herself into custody, one of the men turned on him. "He hit me with the butt of his gun and they pushed her into a car and took her."
Her destination was a cell in the notorious Kaliti prison outside the capital Addis Ababa. It's a place with which she is already intimately acquainted, where prisoners are kept in conditions she once described as "dehumanising", "atrocious" and "barbarous".
The UK director of Amnesty International, Kate Allen, said: "There appears to be no lawful reason why Birtukan Mideksa was arrested or remains in detention. She has now been held for a month in solitary confinement and still has not been charged. This is unacceptable."
Ethiopia's Prime Minister, Meles Zenawi, has been in power since 1995. He was formerly feted as a progressive voice by Tony Blair but he has become markedly dictatorial during his years in power. One regional analyst said the government was becoming increasingly paranoid.
"This came in the context of an election that the government lost control of in 2005, and ahead of 2010 elections that it fully intends to keep from going the same way."
Recently, laws have been passed to heavily restrict the work of international non-government organisations, despite an ongoing famine in areas of the country. "Much of the government's behaviour stems from security concerns, and a lack of understanding that improving human rights will actually help to mitigate many of their concerns," said the analyst.
Professor Woldemariam, one of a few people still prepared to speak out in a country he describes as a "police state", says the regime had become frightened of Ms Mideksa. "They are looking for any excuse to get her because she's a dynamic girl who is getting increasingly popular. They want to cut her short."
But it will not be easy to intimidate her, he believes. "She has such faith in the law. She says to me, 'the law says this, the law says that ...'. I said to her: 'What law are you talking about? You were locked up for two years with no due process.'"
Described as an "Ethiopian Obama" and a brilliant speaker and organiser, she has become a symbol of democracy in her own country, compared with figures like Burma's Aung San Suu Kyi.
There is reported to be deep disquiet among the general population at her arrest and conditions of detention, even though their dissent is not tolerated. Ethiopia, largely Orthodox Christian, has been a staunch ally of the American-led war on terror and a partner in its disastrous policy on Somalia.
The arrest of Ms Mideksa has sparked criticism from some American senators and the hope that the Obama administration might change Washington's relationship with the Zenawi government.
"There is no democracy in Ethiopia today, despite empty claims of 'recent bold democratic initiatives' taken by our government," Ms Mideksa told US senators.
Many in Ethiopia and its large diaspora are hoping that Mr Obama's offer to "extend a hand" to dictatorships who would unclench their fists included a message to Addis Ababa.
Ms Mideksa has already given Washington her advice: "Ethiopia has many problems, including a legacy of repression, corruption and mismanagement. The US can help by using its considerable influence to encourage the government to negotiate with the opposition. It will not be easy to confront the past.
"We must start at the right point by embracing the rule of law, human rights and democracy."
Views from cyberspace: What the blogs say
*There is an old Ethiopian proverb which in translation says, "Oh, Mr Hyena, don't give me excuse to eat me". (
Aya jibo sata mehagne blagne). Why is Zenawi resorting to such thuggish tactics against Birtukan? And Professor Mesfin? And the [Unity for Democracy and Justice Party]? Is he trying to create a convenient distraction from his devastating defeat in Somalia? - Quatero News and Views
*Birtukan has modelled courage and conviction. I do not think she is asking the Ethiopian people to personally rescue her; but instead, on behalf of others. - Anyuak Media
* Birtukan Mideksa continues to impress millions of her fellow compatriots to promote the struggle forthe triumph of democracy over tyranny. - Ethiomedia
*In fact, the Ethiopian tyrant has killed far more innocent people than the Zimbabwean tyrant. The Ethiopian tyrant also has rigged national elections for three times like the Zimbabwean tyrant. I hope and I believe democrats as well as President Obama will restore respect for the US by supporting people who aspire for their democratic rights. - Shemolo
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