Anwar, who is the most potent threat to Prime Minister Najib Razak, had appealed against charges of sodomising his former aide Mohd Saiful Bukhari Azlan in 2008 but the Federal Court ruled yesterday that there was overwhelming evidence against the 67-year-old leader.
The decision was sharply criticised by the US, Australia and human rights organisations.
"I have fought for most of my life on behalf of the people of this country. For the people, I am willing to go to jail or face any other consequence.
"As Allah is my witness, I pledge and I will not be silenced. I will fight on for freedom and justice and I will never surrender," he said in a statement here.
Meanwhile, Anwar's second daughter Nurul Nuha has said she will lead an international 'March to Freedom' campaign for her family to free the opposition leader.
"As his children, we will take over his mantle and continue his struggle, hopes and ambition," the 31-year-old said.
"These 17 years have been an emotional roller coaster. We do not know how long this struggle will continue but we will be with our father till the end," she told reporters before breaking down in tears.
Anwar has accused the judges of not having given proper consideration to the case presented by his counsel.
"Yes, you have passed judgement on me and I will, for the third time, walk into prison but rest assured, my head will be held high.
"The light shines on me," he said in a statement.
Describing the case as a "complete fabrication from a political conspiracy to stop his political career", Anwar warned that legal students and professors would dissect the judges' reasoning and tear their judgement into "tatters".
Meanwhile, police detained a cartoonist called Zulkiflee Anwar Alhaque, also known as Zunar, last night over a series of tweets on Anwar's case.
A cartoon he posted on Twitter showed Prime Minister Najib Razak as the judge in Anwar's case.