Since Rankin is the British queen's representative in Bermuda, his assent was necessary to put the legislation into effect. The supreme court ruling spurred celebrations within the small gay community in the island but also enraged the socially conservative population in the territory.
In a statement, Greg wrote, "As we all know, equality doesn't happen overnight, it takes time, it takes fearless individuals to stand up for what's right regardless of what society says".
She said that after "full and careful consideration" of Bermuda's constitutional and global obligations, Johnson had decided that it would "not be appropriate" to block the legislation, something she said only took place in exceptional circumstances.
"But that Bill has been democratically passed by the Parliament of Bermuda, and our relationship with the overseas territories is based on partnership and respect for their right to democratic self-government".
Responding, Bryant said this was not good enough.
He denounced the move as a "backwards step for human rights in Bermuda and in the overseas territories".
"Gay and lesbian Bermudians have been told that they aren't quite equal to everyone else".
The decision represents the first reversal of a trend among Western countries of legalising same-sex marriage.
Mr Pettingill - a former Attorney-General who represented Winston and Greg Godwin-DeRoche in their case which resulted in the Bermuda Supreme Court making same sex marriage legal in May 2017 - was speaking after the Governor gave assent to the Domestic Partnership Act 2017.
About 63,000 people live in Bermuda, according to the island's government.
Baldwin came under pressure over the issues from MPs from a series of parties, including the Conservative Nigel Huddleston, the SNP's Carol Monaghan and Jamie Stone of the Liberal Democrats.
Foreign Office Minister Harriett Baldwin said "after full and careful consideration" the government had decided not to block the legislation.
The British government could have blocked the territory from enacting the law, the BBC reports, but chose not to.
Same-sex marriage and civil unions were voted on in a non-binding referendum in June 2016. Both proposals were rejected by voters, but the turnout was below the 50% requirement.
Bermudian Minister of Home Affairs Walton Brown says the move has "protected the rights of same-sex couples" whilst "restating that marriage must be between a male and a female".
LGBT+ civil rights groups said that domestic partnerships amount to a second-class status and that it is unprecedented for a jurisdiction to take away the legal right to marriage after it has been granted.
Now, less than a year later, the island-nation's Governor John Rankin just signed a Bermuda gay marriage repeal replacing same-sex marriages with "domestic partnerships" which can be entered into by both different-sex and same-sex couples.
Despite a Supreme Court ruling previous year authorizing same-sex marriages, Bermuda's governor approved a bill reversing the right of gay couples to marry.