Canon Jim Pannett, 75, who on Saturday marked 50 years of priesthood, said the issue of same-sex marriage has become "in your face" and that it contradicts the Bible's teachings.
The head of St John the Baptist Catholic Church in Dale Road, Purley – who teaches children in services and assemblies at six local schools including John Fisher and St Thomas More – oversees a 1,500-strong congregation and was responsible for organising Pope John Paul II's 1982 visit to London.
Speaking of his stance, Canon Pannett said: "It is taken on board and recognised but not welcome. It goes against the tradition of the Church and its teachings. When I started my training in 1962, no one would have even thought to mention the issue."
The leader's comments reveal how divided Croydon's religious community is following a number of high-profile public debates over the issue.
Last month, Croydon Central MP Gavin Barwell hosted a public meeting at Croydon Town Hall attended by religious figures to discuss same-sex marriages while the Government explores the possibility of legalising it.
The Rev Art Lester, head of the church of Croydon Unitarians, branded Canon Pannett's comments "ignorant".
He said: "Nobody has the full story and therefore the right to impose dogmatic rules on anyone else. We see this as a form of ignorance that in 50 years' time will seem ridiculous to the people who once believed in it. These people continue doing more harm than good and they should have their knuckles wrapped for it. I find them predictable and intolerant. We have been doing same-sex legal blessings for more than 50 years."
The Advertiser last month reported how an Anglican preacher at All Saint's Church in Sanderstead had encouraged his congregation to sign a petition against same-sex marriage.
Peter Gowlland, 78, a lay reader at the church, had reportedly asked the congregation to be "bold like the Apostles" and sign the Coalition For Marriage petition.
Croydon councillor Wayne Lawlor, who is in a civil partnership but cannot get married to his partner in England or the US, said: "The Catholic Church needs to come into the 21st century and leave the medieval ages behind. I take the line that their comments are based on intolerance and narrow-mindedness, but I respect their right to believe in whatever they want to."
Ross Burgess, secretary of the Croydon Area Gay Society, said: "Clearly the Catholic Church is opposed to gay marriage and wouldn't want to conduct them. But I do know Catholics who are not completely opposed to it. No one is going to force the Catholic Church to conduct same-sex marriages. I think that would be wrong in terms of religious freedom, but given there are some religions that would like to, they should be able to."
Gay people who form civil partnerships are now entitled to the same property rights, exemptions on inheritance tax, social security and pension benefits, and can also get parental responsibility for a partner’s children.
A civil partnership is formed when a same-sex pair register as civil partners of each other, ending only in death, dissolution or annulment, in the presence of a registrar and two witnesses while signing the civil partnership document.
Prime Minister David Cameron suggested the Government is planning to legalise gay marriage after telling a Tory conference in Manchester last year: "I don’t support gay marriage in spite of being a Conservative. I support gay marriage because I am a Conservative."
The legal implications remain unresolved.
Churches may be forced to accept gay ceremonies as those who refuse to conduct them could face legal challenges under existing rights legislation.
However, it is thought most gay couples would opt not to be married in a place of worship.
It is currently prohibited for any religious readings, music or symbols to be included in civil partnership ceremonies.