Holder's declaration underscored President Barack Obama's break with the former Bush administration's anti-terrorist policies, which were condemned by human-rights groups, civil liberties advocates and U.S. allies abroad.
"Waterboarding is torture ... My Justice Department will not justify it, will not rationalize it and will not condone it," Holder, who his heading a review of the treatment of terrorism suspects, said in a speech to the Jewish Council of Public Affairs in Washington.
"Too often over the past decade the fight against terrorism has been viewed as a zero-sum battle with our tradition of civil liberties. Not only is that school of thought misguided, I fear that in actuality it has done us more harm than good," Holder said.
"We cannot ask other nations to stand by us in the pursuit of justice if we are not viewed as being in pursuit of that ideal ourselves," he said.
One of the most widely condemned Bush administration practices was waterboarding, a form of simulated drowning, which the CIA has acknowledged using on three terrorism suspects before it said it stopped the practice in 2003.
Ban on ‘Waterboarding’
Bush administration officials had stopped short of categorically ruling out its use in the future.
Obama in January ordered that government agencies must abide by interrogation limitations in the Army Field Manual, which bans waterboarding.
But he also asked for a review of detention and interrogations practices, which some human rights critics said left open the possibility that some forms of harsh interrogations could be later approved.
Holder said that although many practices would be subject to review under Obama's executive orders, "one in particular (waterboarding) will absolutely not be."
Obama, who took office on Jan. 20, reiterated in a speech to Congress last week his campaign promise to set a new course in counterterrorism policies.
"Living our values doesn't make us weaker, it makes us safer and it makes us stronger. And that is why I can stand here tonight and say without exception or equivocation that the United States of America does not torture," Obama said.
At the same time, he vowed "swift and certain justice for captured terrorists."
The Democratic president has also ordered the closure of the U.S. detention center at Guantanamo Bay, Cuba, where many foreign terrorism suspects have been held for years without trial.
