Swedish authorities want to extradite the whistleblower for alleged sex offences but his lawyer argued the comments made this week could damage his chance of a fair trial.
Speaking on the final day of his extradition hearing, Geoffrey Robertson QC, told Belmarsh Magistrates' Court in south east London that Sweden's prime minister had made an attack on Assange and his defence counsel.
He said: "He has effectively been denounced as an enemy of the people."
Prime minister Fredrik Reinfeldt's remarks were said to include claims that Assange and his lawyers had been "condescending and damaging to Sweden" and to have implied that they thought women's rights were worthless.
Mr Robertson said: "In a small country...it has created a toxic atmosphere, media are reporting it and it is a basis for comment.
"Mr Assange is public enemy number one as a result of the prime minister's statement.
"People will believe...that Mr Assange has been damaging Sweden."
He described it as an "intolerant development" in the case and accused the head of state of showing "complete contempt for the presumption of innocence".
But Clare Montgomery QC, for the Swedish authorities, dismissed the notion that the prime minister had vilified Assange, suggesting that the comments were a reaction to media briefings given by the defence outside court.
She said: "You might think those who seek to fan the flames of a media firestorm can't be surprised when they get burnt."
Assange faces three charges of sexually assaulting one woman and one charge of raping another during a week-long visit to Stockholm in August.
He denies committing any offences and his supporters claim the criminal inquiry and extradition request are unfair and politically motivated.
Mr Reinfeldt's remarks followed two days of evidence presented by the defence earlier this week, which included implicit criticism of the country's justice system.
But the prime minister's intervention was "extraordinary", Mr Robertson said, since he had previously indicated he thought it would be inappropriate for him to comment on the case.
"Why then, only...days later, does he launch a full-bloodied assault on Mr Assange and his defence in these proceedings?" he said. "Was it political motives?"
Nor was the prime minister the only Swedish politician to have weighed in, he told the court.
"It doesn't stop there," he said. "I've seen a report about the chancellor jumping in to endorse the prime minister's remarks."
But District Judge Howard Riddle refused to grant Assange's lawyers more time to prepare evidence on the potentially damaging impact of the prime minister's comments.
He said: "In a case such as this there are always likely to be further developments."
An "element of finality" was needed in the proceedings, he went on, adding that he expected any decision made on extradition to be appealed against. .
Summing up, Mr Robertson told the court:
:: If Swedish prosecutor Marianne Ny's statements were to be given "evidential weight", she should have come to testify herself;
:: Assange volunteered to be questioned in Sweden on August 30 but the prosecutor refused to interview him then;
:: The 39-year-old Australian had also offered to be interviewed from abroad by phone, video link and Skype, but had been turned down;
:: Rape trials in Sweden were "secret" and heard behind closed doors and that what Assange was accused of would not amount to rape anywhere other than in Sweden anyway.
On top of this, the prime minister's statement had served as an "extraordinary own-goal because it shows beyond doubt that he won't get a fair trial in Sweden", he added.
Ms Montgomery countered that the warrant had been issued for prosecution; that one of the alleged offences would amount to rape in English law as well as in Swedish law; and that there would be no "secret trial", but rather one in which the evidence is heard in private but the arguments about it are made in public.
The matter was adjourned to February 24, when Judge Riddle is expected to announce his decision on whether Assange should be extradited.
Speaking outside court afterwards, Assange pointed out that Ms Montgomery had represented Chile's former military ruler General Augusto Pinochet in his extradition hearing at the House of Lords.
He went on: "In this case ... we have not been able to present my side of the story. I have never been able to present my side of the story."
But he hoped his plight would serve to highlight abuses suffered by others in similar positions who did not benefit from the same media spotlight, he said.
"What gives me hope is that we can prove this particular case and not simply draw attention to the difficulties and pressures that we and other people have been under but perhaps we will have an opportunity to set a new precedent about the abuses of the European Arrest Warrant," he said.
"We have an opportunity perhaps to draw attention to all those people who do not have the luxury of this press to scrutinise what's happening to them."
Among such people, he said, were the thousands of Poles being extradited to Poland.
His case also provided an opportunity to draw attention to "some of the problems that people in Sweden are demanding the world's attention on", he added.
These, he claimed, included abuses of process, secret trials and the lack of effective remedy for abuse.
His lawyer, Mark Stephens, added that the Swedish prime minister's intervention was "wholly inappropriate".
He said: "In any decent country the rule of law is separate from the political process. In Sweden it is not."
He described this as "one more example of the quite exceptional behaviour in the Julian Assange case".
