"Faced with conditions of near total isolation... I am satisfied that the procedures (outlined by US authorities) will not prevent Mr. Assange from finding a way to commit suicide."
Lawyers for the US authorities are expected to appeal against the decision.
US prosecutors and Western security officials regard Assange, the founder of WikiLeaks, as a reckless and dangerous enemy of the state whose actions put at risk the lives of agents whose names were in the material.
The US authorities say more than 100 people were put at risk by the disclosures and about 50 had received assistance, with some fleeing their home countries with their spouses and families to move to the United States or another safe country.
Supporters regard him as an anti-establishment hero who has been victimised because he exposed US wrongdoing in wars in Afghanistan and Iraq, and say his prosecution is a politically motivated assault on journalism and free speech.
Baraitser rejected this, however, saying there was insufficient evidence that prosecutors had been pressured by Trump's team and there was little evidence of hostility from the US president towards him.
She said there was no evidence that he would not get a fair trial in the United States or that prosecutors were seeking to punish him, and said his actions had gone beyond investigative journalism.