The Scottish Conservative leader’s intervention will increase the pressure on Theresa May to press for a change in the law in Northern Ireland, which is the only part of the UK where same-sex marriage is still illegal.
The issue has come to the fore since the Prime Minister’s decision to sign a £1bn deal with the DUP in return for its support at Westminster, which gives the Government a narrow majority.
Ms Davidson also said she supported Saturday’s march in Belfast, which is expected to see thousands of people on the streets calling for gay marriage to be introduced by Stormont.
“Northern Ireland is the only part of the UK where equal marriage is still prohibited. I’ve campaigned passionately for this to change,” she wrote in a column in the Times newspaper.
“I’ve raised the issues with Arlene Foster, leader of the DUP, and have sought and received assurances from the prime minister that the Conservative Party will use our influence to press for marriage equality.”
The DUP has scuppered any change in the law despite a majority of MLAs supporting a move towards equal marriage at the most recent vote.
The party has denied being homophobic, insisting it is instead protecting the “traditional” definition of marriage.
In a further apparent dig at Northern Ireland’s largest party, Ms Davidson highlighted her intention to marry her partner Jen Wilson, a Catholic Irishwoman.
“I am a practising Christian,” she wrote. “I am a protestant. I am a unionist. I am Scottish and British.
I am also engaged to a Catholic Irishwoman from County Wexford, who was educated by nuns.” The leaders of Scotland’s other political parties have also called for the introduction of same-sex marriage in Northern Ireland ahead of today’s march.
First Minister Nicola Sturgeon of the SNP, Labour’s Kezia Dugdale, Patrick Harvie of the Green Party and Liberal Democrat Willie Rennie all said they wanted to see the law change.
Ms Sturgeon said the introduction of gay marriage in Scotland had helped to “challenge negative attitudes” towards LGBTI people, while Mr Rennie said it had “brought joy to many lives”.
Ms Davidson is the most senior Tory to publicly challenge the Government’s DUP partners over the issue – but the SNP questioned whether she would be able to influence Mrs May.
“We of course welcome any steps taken to increase equality – but given the Scottish Tories’ recent track record, these ‘assurances’ ring hollow,” said Christina McKelvie, the SNP MSP and convenor of the Scottish Parliament’s Equalities and Human Rights Committee.
“If Ruth Davidson was really unhappy about the government being propped up by the dinosaurs in the DUP, her MPs could have done something about it.”