He was educated at Winchester College and Cambridge University, where he read literature.
He went on to teach in Africa and converted to Catholicism in 1971.
He joined the ultraconservative Society of St Pius X, a conservative Catholic group that opposes the liberal reforms introduced by the Church in the 1960s under the Second Vatican Council.
He was excommunicated by Pope John Paul II in 1988 after being "illicitly" ordained as a bishop by the breakaway French Archbishop Marcel Lefebvre.
Since 2003 he has been rector of the Society of St Pius X's Seminary of Our Lady Co-Redemptrix in La Reja, Argentina.
In an interview with the Catholic Herald, Williamson said that he himself was not an anti-Semite, but didn't like "adversaries of Our Lord Jesus Christ".
He said: "If Jews are adversaries of Our Lord Jesus Christ $ obviously not all of them, but those that are $ then I don't like them.
He has claimed that the 9/11 attacks on the US were carried out by the American military in order to justify the invasions of Afghanistan and Iraq. The Twin Towers were brought down not by hijacked airliners but by American missiles or demolition charges, he believes.
He has also endorsed the "Protocols of the Elders of Zion", a notorious anti-Semitic forgery that enjoys widespread currency in neo-Nazi circles.
He is also on record as saying that Jews are fighting for world domination "to prepare the anti-Christ's throne in Jerusalem".
In an interview with Swedish TV broadcast last month, he said: "I believe there were no gas chambers." He insisted that up to "300,000 Jews perished in Nazi concentration camps but none of them by gas chambers". He maintained that historical evidence "is hugely against 6 million Jews having been deliberately gassed."
