Theresa May and Leo Varadkar attend Lyra McKee's funeral

The funeral of Lyra McKee, the journalist shot dead in Derry last week, brought a rare political unity to Northern Ireland on Wednesday.

Theresa May joined dignitaries including the Labour leader, Jeremy Corbyn, the Irish PM, Leo Varadkar, the Irish president, Michael D Higgins, and the Irish minister for foreign affairs, Simon Coveney, at the funeral.

The New IRA shot McKee, 29, while she observed rioting in Derry last Thursday. The group has apologised and said its gunman was aiming at police.

Lyra McKee.Photograph: Family handout/PA

The Northern Ireland secretary, Karen Bradley, and leaders of Northern Irish political parties are also at the service, which started at 1pm at St Anne’s Cathedral in central Belfast.

McKee’s death has prompted calls for the leaders of Sinn Féin and the Democratic Unionist party (DUP) to restore power-sharing, which collapsed in acrimony in 2017, leaving a political vacuum.

McKee’s north Belfast family is from a Catholic background but chose a Protestant cathedral because it wanted a cross-community, cross-border and multi-cultural service.

The service is led jointly by Stephen Forde, the dean of St Anne’s, and Fr Martin Magill, a Catholic priest. Members of the National Union of Journalists are to form a guard of honour. McKee is due to be buried later on Wednesday at Carnmoney cemetery.

McKee’s partner, Sara Canning, said the service would celebrate the life of the author and LGBT activist. She invited mourners to wear costumes of characters beloved by McKee. “If people would like to wear Hufflepuff, Harry Potter or Marvel-related T-shirts I know she would love it,” Canning said.

McKee is survived by her mother, two brothers and three sisters. The family said in a statement she was a friend to all who wished ill on no one. “Such a warm and innocent heart, she was the greatest listener, someone who had time for everyone. She was a smart, strong-minded woman who believed passionately in inclusivity, justice and truth.”

The family said the outpouring of support had been a solace and expressed hope the shock of her death would unite people. “We would ask that Lyra’s life and her personal philosophy are used as an example to us all as we face this tragedy together. Lyra’s answer would have been simple, the only way to overcome hatred and intolerance is with love, understanding and kindness.”

Leo Varadkar, Theresa May and Irish president Michael D Higgins.Photograph: Brian Lawless/PA

McKee’s murder has prompted a backlash against the New IRA and its political allies in the fringe party Saoradh, which means Liberation in Irish. Activists smeared red handprints on the party’s Derry office.

There have been vigils across Northern Ireland and in Dublin. Journalists, LGBT activists and others in London were due to hold a minute’s silence in Fleet Street to coincide with the funeral.

Theresa May’s attendance at the service meant her deputy, David Lidington, was taking prime minister’s questions in the House of Commons.

Friends arrive for the funeral service.Photograph: Liam McBurney/PA

Northern Ireland’s political parties have called a de facto truce in the region’s toxic, dysfunctional politicking. Sinn Féin and DUP leaders appeared together in Derry after the killing, drawing praise and encouragement to start talks on restoring power-sharing.

Colum Eastwood, leader of the SDLP, the moderate nationalist party, urged politicians to seize the moment. “There is an unmistakable public desire that the tragic and terrible loss of Lyra McKee marks a turning point for our peace and political process,” he said in a statement.

The New IRA cites political deadlock in Northern Ireland as evidence of the state’s illegitimacy and considers the peace process a dead end for a united Ireland.

A mourner wearing a Hogwarts scarf holds the order of service for McKee’s funeral.Photograph: Charles McQuillan/Getty Images

The Sinn Féin leader, Mary Lou McDonald, told the BBC on Wednesday it was a tiny, unrepresentative group. “The war in Ireland is over, the conflict is over, the IRA arms have been destroyed or put beyond use. We have a new democratic dispensation and it is so important we make that work, that institutions of government work.”

Analysts are sceptical McKee’s death will break Northern Ireland’s deadlock. Brexit, a pending report into the cash-for-ash scandal and next week’s local elections are aggravating lack of trust and cooperation between Sinn Féin and the DUP.