Same-sex couples will be able to marry in the Isle of Man, 24 years after gay sex was decriminalised on the island.

A new law from Friday will also allow heterosexual couples to have civil partnerships instead of marriages if they prefer.

The Isle of Man’s marriage (same sex couples) bill 2016 was promoted by Allan Bell, the island’s chief minister, who has been in a gay relationship for over 20 years. “This has been a long, long journey,” Bell, 69, told the Guardian this week. “This bill gives equal validity to relationships between same-sex couples as heterosexual ones and proves that the love of two people will overcome everything.”

Bell said he had no plans to marry his partner imminently but that he hoped there would be a queue outside the register office on Friday, as well as religious institutions not exempt from the act.

Church of England ministers do not have to marry gay couples under the new law. The island’s bishop, who sits in the Manx parliament’s upper chamber, was one of a handful of representatives to oppose equal marriage.

The bill was welcomed by the island’s LGBT community, including Alan Shea, who in 1991 caused outrage on the island by dressing as a concentration camp inmate on an important national holiday to draw parallels with Nazi persecution of homosexuals. One man called him a “bum blaster” on camera during the stunt on Tynwald Day, while soldiers could be heard hissing at him en masse. At that point, anyone caught having gay sex faced life in prison.

Shea said he was delighted, if surprised, at the new law. “I’m still in shock that it’s come through,” he said. “I never thought it would actually happen, when you think how things were just 25 years ago, when you consider the hatred and bigotry we used to face.”

Bell was one of a number of politicians who faced insults in the House of Keys, the directly elected lower branch of Tynwald, the parliament of the Isle of Man, when arguing for decriminalisation of homosexuality. In one particularly fraught session a politician said that to legalise gay sex would “lead to a charter for wimps and perverts to further infect society”.

Shea and his partner, Stephen Moore, entered into a civil partnership four years ago. They plan to swap it for a marriage in the new year. “We’ll let the younger ones who haven’t already got a civil partnership go first,” he said. Shea’s concentration camp costume (actually striped pyjamas from Marks & Spencer) is now in the Manx museum.

Moore said Bell deserved enormous credit for advocating gay rights throughout his 30-year political career, but said: “Politicians may have been persuaded but the battle for hearts and minds goes on.”

The bill was passed in April by the Tynwald, the Isle of Man’s parliament, but needed to be rubber-stamped via the Queen. Although the Isle of Man is not part of the United Kingdom, it is a crown dependency, so the reigning monarch must still grant royal assent via the privy council. The Queen granted the bill royal assent last Wednesday, a spokeswoman for the privy council said on Monday. A few formalities must then be completed in order for the new act to come into force on Friday.

The new law was welcomed by the human rights advocate Peter Tatchell, who last year lobbied the Isle of Man chief minister to legislate equality in civil marriage and civil partnership law. “Congratulations and thanks to the people and government of the Isle of Man. Their new legislation is even more progressive than the UK. Instead of segregated marriage laws for gay and straight couples, they have a single civil marriage law that applies to everyone regardless of sexual orientation,” he said.

“The Isle of Man has also opened up civil partnerships to opposite-sex couples; in contrast to the ban that exists in England, Wales, Scotland and Northern Ireland. These changes catapult the Isle of Man to the forefront of legal equality for straight and gay couples.”