In interviews on Tuesday on the eve of the fifth anniversary of the invasion, the three said they have lived more modestly without government salaries but the chaos that has followed President George W. Bush's Iraq policy shows their actions were justified.
"The decision I took was the best decision I've ever made in my life," said John Brady Kiesling, 50, who had served as a political officer in Greece, Armenia and Morocco.
Kiesling was the first diplomat to go public with his dissent, publishing his resignation letter to then-Secretary of State Colin Powell. Powell's reputation was to be tarnished by his public embrace of the war, while Kiesling became a rare diplomat whose private opinions garnered public attention.
"Our fervent pursuit of war with Iraq is driving us to squander the international legitimacy that has been America's most potent weapon of both offense and defense since the days of Woodrow Wilson," Kiesling wrote in his resignation letter.
The war did lead to the hanging of Iraqi leader Saddam Hussein but officials never found weapons of mass destruction that the Bush administration had cited as a key reason for the invasion and many nations denounced the U.S.-led war.
Now a resident of Athens, Greece, Kiesling and two others that followed him in resigning, John Brown and Mary Ann Wright, said leaving their diplomatic careers had been hard.
"I've had to tighten my belt," said Brown, 59, who served in London as well as Moscow, Prague and Belgrade. "I have to be very careful about my budget."
Wright, 61, who helped reestablish the U.S. Embassy in Kabul, Afghanistan, in 2001, has become active in the anti-war movement. She relies on the hospitality of others as she travels to rallies and events.
Kiesling says he lives in a modest one-bedroom apartment and relies on a bicycle and walking to get around.
All three remain engaged in public policy issues but say it was not always easy to start afresh in middle age.
"There is something terrifying about no longer having an identifiable role in the world," Kiesling said. "I was part of a very clear social hierarchy. I knew my place, and that's very comforting."
Kiesling taught at Princeton University for a year and in 2006 published the book "Diplomacy Lessons: Realism for an Unloved Superpower." He is now researching a book on a Greek terrorist group.
Brown, who said he was inspired to go public after Kiesling's resignation, said he wanted the world to know some diplomats dissented. Looking back, he said: "I have my reservations on what impact, if any, it had on policy."
Brown has taught at Georgetown University in Washington, written frequently and maintained a blog on diplomacy.
While Kiesling and Brown have focused on academic work, Wright, who served in the military for 29 years before joining the Foreign Service, has focused on the anti-war movement and published "Dissent: Voices of Conscience."
Before her resignation, she sent a cable in the State Department's dissent channel, a mechanism set up during the Vietnam War in 1971 for internal disagreements. She received a stock reply and then decided to go public.
"It was a big step. I was pretty senior in rank, just below ambassador," said Wright, a former deputy chief of mission in Mongolia who moved to Hawaii to be far from Bush's Washington.
"My whole life has really changed," she said. "Most of my life is dedicated to trying to stop the war."
The three former diplomats did not know each other before, but have written a joint opinion article they hope to publish on Wednesday's anniversary.
"The war happened, with tragic but predictable consequences," they wrote. "The invasion of Iraq had a terrible impact on America's relationship with the world."
"Our gesture earned us a brief moment in the media and the cautious respect of our colleagues. Five years later, we do not regret our decision to leave the profession we loved."
Editing by John O'Callaghan
© 2008 Reuters