Amnesty International denounced Sheikh Nimr's trial as "political and grossly unfair."
Some have warned that the Saudis are on the brink of a theological civil war pitting the larger and far stronger Sunni states against the Shiites. The Sydney Morning Herald foreign editor, Maher Mughrabi, writes that the West may find itself dragged into the violence.
"For Shiites around the world, Nimr is the latest in a long line of martyrs at the hands of tyrannical rulers. They will recall the proverbial utterance of their inspiration, the Prophet Muhammad's son-in-law Ali bin Abi Talib, that "the day of the oppressed over the oppressor is more severe than the day of the oppressor over the oppressed".
"In Egypt, the Arab Spring brought democratic elections and the downfall of long-serving dictator Hosni Mubarak. The Saudis were amazed and appalled when their allies in Washington proved unwilling to back Mr Mubarak to the hilt. They were even more horrified when the Obama White House pursued dialogue and a deal with Iran over its nuclear program.
"The Saudi response has been to freelance a new, far more aggressive policy across the region, leading a coalition to invade and bombard Yemen and bankrolling the return of military rule in Egypt, which is now effectively a wholly-owned subsidiary of Saudi Arabia."
"The voices of all those in the Middle East who argue for a civic space that allows opposition voices and demands accountability from rulers have been weakened by this draconian act.
"More worryingly, the voices of those who argue that the sword of the state only understands one language - that fire can only be fought with fire - have been strengthened, making bloodshed and violence more likely not only for Saudi Arabia and its interests around the world but for all those who are allies and business partners of the House of Saud. And that could mean many Western countries."
"Whether we like it or not, the bell that tolled for Nimr Baqir al-Nimr tolls loudly for all of us. We cannot afford to let it pass unheeded."