Cardinal Keith O'Brien, Britain's most senior Roman Catholic cleric, has resigned with immediate effect in the wake of allegations of inappropriate behaviour, he said in a statement on Monday.
O'Brien, who as Archbishop of St Andrews and Edinburgh was leader of the Catholic Church in Scotland, denies allegations that he made sexual advances towards priests in the 1980s.
He had been due to be the only cardinal from Britain to vote on a replacement for Pope Benedict XVI following the pontiff's shock resignation on February 11.
But O'Brien confirmed that he would not now take part in next month's conclave.
"I will not join them for this conclave in person," he said. "I do not wish media attention in Rome to be focused on me -- but rather on Pope Benedict XVI and on his successor."
In his resignation statement, O'Brien said: "Looking back over my years of ministry: for any good I have been able to do, I thank God.
"For any failures, I apologise to all whom I have offended."
O'Brien had been due to resign on his 75th birthday next month, but he said: "The Holy Father has now decided that my resignation will take effect today, 25 February 2013."
The allegations include claims that one priest received unwanted attention from O'Brien after a late-night drinking session, Britain's Guardian newspaper reported.
Another priest reportedly claims that O'Brien used night prayers as cover for inappropriate contact.
O'Brien has previously angered the gay community with his hardline public stance on homosexuality. He was named "bigot of the year" last year by the gay rights charity Stonewall.
He recently said that same-sex marriages would be "harmful to the physical, mental and spiritual well-being of those involved" and has long voiced opposition to gay adoption.
But in comments this week he also called for the Catholic Church to end its celibacy rule for the priesthood.
A string of new scandals and allegations have emerged since Benedict became only the second pope in the Church's 2,000-year history to step down of his own free will.
Four members of the conclave are associated with the paedophile priest scandals that have dominated the German pope's eight-year rule.
Thousands of American Catholics have signed a petition calling for US cardinal Roger Mahony, accused of covering up for paedophile priests in Los Angeles for years, to give up his vote in the conclave.
And while 85-year-old Benedict cited his age as the main factor in his resignation, media have speculated that an explosive report into last year's "Vatileaks" scandal may have played a role.
The scandal saw Benedict's butler arrested, convicted and later pardoned for leaking confidential papers to the press.
The Vatican said on Monday that the report on the scandal, which exposed intrigue and corruption in the Church, would be shown exclusively to the future pope.