Wilders, who faces prosecution in the Netherlands for anti-Islam remarks, came to London after winning an appeal earlier in the week against a ban on him entering Britain.
Scores of police formed a barrier between a group calling itself "Islam in the UK" and Wilders' car as the protesters waved banners reading "Sharia for the Netherlands" and shouted "Wilders go to Hell" and "Muslims rise up."
Wilders was barred in February because British ministers said his presence would threaten community harmony and public safety.
"Being here today in the United Kingdom is a victory, it's not so much a victory for myself, because I am not that important, but it is a victory for freedom of speech," he told reporters. "It is ridiculous that the UK government thought that my presence would in any way lead to violence."
Wilders had planned to speak to the media on a green outside the palace of Westminster but was forced to hold it inside a nearby parliamentary office on advice of police.
Wilders came to London at the invitation of UK Independence Party peer Lord Malcolm Pearson to discuss showing his film Fitna in parliament. The film, which argues the Koran incites violence, urges Muslims to tear out "hate-filled" verses from the Koran.
"I have nothing against Muslims, I know the majority of Muslims in our society are law-abiding people," he said. "I have a problem with the Islamic ideology, the Islamic culture because I believe that the more Islam we get in our free societies, the less freedom we will get," he added.
Outside the building, protesters used a loudspeaker to noisily vow to bring Sharia to the whole world.
"This man is an enemy of Islam and of Muslims and the British government is well aware of this and this just gives rise to so-called extremism," one protester," Abu Muaz, told Reuters.
On Tuesday, Britain's Asylum and Immigration Tribunal overturned the ban on him entering the country following a challenge by Wilders.
A Home Office spokesman on Friday said, "We are disappointed by the court's decision. The government opposes extremism in all its forms." He said authorities will monitor Wilders during his stay in the UK, which could affect future decisions on whether to allow him entry.
