A priest received a standing ovation at Lyra McKee's funeral when he asked why it took her death to unite politicians.
Politicians attended a vigil in Londonderry after her murder, and also her funeral in Belfast on Wednesday.
Fr Martin Magill asked: "Why in God's name does it take the death of a 29-year-old woman with her whole life in front of her to get to this point?"
However, DUP MP Sammy Wilson said he was not convinced it marked a turning point to restore power-sharing.
Ms McKee was shot dead on Thursday as she observed rioting in the Creggan area of Derry.
A dissident republican paramilitary group, the New IRA, said its members killed her.
Prime Minister Theresa May, President of Ireland Michael D Higgins, Taoiseach (Irish prime minister) Leo Varadkar and other politicians were at the service.
A friend told mourners at her funeral that Ms McKee revealed her plans to propose to her partner Sara Canning just hours before she was murdered.
Stephen Lusty said she showed him pictures of the engagement ring.
"She showed me pictures of the ring she had bought for Sara and told me of the fabulous plans she had of her proposal in May," said Mr Lusty.
"She made me put a date in my diary for the wedding in Donegal in 2022 and gave me strict instructions to wear my kilt, which she always wanted to borrow, adorn it with some Harry Potter."
'Sort it out now'
By Mark Simpson, BBC News NI
Political leaders from Belfast, Dublin and London, all under the one roof.
The disagreements over Brexit and the return of the Stormont Assembly were put into context by matters of life and death.
But those political disputes were not forgotten; quite the opposite.
The message from the pulpit to political leaders in Northern Ireland was clear - sort out your differences now, don't wait.
The funeral took two hours. Those involved in the service hope its impact will be long lasting and far reaching.
Ms McKee's sister, Nichola Corner, told mourners: "In the words of Lyra herself, we must change our own world, one piece at a time. Now let's get to work."
Hundreds gathered for the funeral of Ms McKee, who was from a Catholic background, at a Protestant cathedral.
The congregation was led by Ms McKee's partner, mother Joan McKee, brothers Gary and David and sisters Joan, Nichola and Mary.
Her family chose the location due to its reputation as a "shared space" in a divided city.
Many friends of the journalist and campaigner for LGBT rights wore Harry Potter-themed T-shirts, scarves and badges to the service. Ms McKee was an avid fan of the series.
At the beginning of the service, the Anglican dean of Belfast, the Very Reverend Stephen Forde, said: "Lyra was a person who broke down barriers and reached across boundaries, this was her hallmark in life, this is her legacy in death.
"She was a child of the Good Friday agreement. She was a primary school pupil in north Belfast when the agreement was signed.
"She grew up to champion its hope for a society that was free from the prejudices of the past."
'Lyra is the future'
Grief and outrage over Ms McKee's murder has sparked hopes there is now momentum to break the political deadlock in Northern Ireland.
Northern Ireland has been without a functioning devolved government since January 2017, when the DUP and Sinn Féin split in a bitter row.
On Wednesday, NI Secretary Karen Bradley said she intended to hold talks with Stormont party leaders in a bid to make progress.
The Democratic Unionist Party's Sammy Wilson told BBC News NI that his party had offered solutions, including a time-limited process running parallel alongside the running of the assembly.
Sinn Féin leader Mary Lou McDonald rejected Mr Wilson's criticisms.
"He knows that the issues that have held us back are issues of equality and recognition," she said.
"This stalemate is not acceptable and we need to act to resolve it."
Three people have been arrested over the murder, and all have been released without charge.
Speaking after her funeral, Northern Ireland's top police officer said Ms McKee "cared passionately about issues and worked hard and with integrity".
"Of course that is in complete contrast to those people who came out of the shadows last Thursday night, fired shots at police lines, hitting Lyra and fatally injuring her," said Chief Constable George Hamilton.
"I suppose the outpouring of condemnation from the communities of Derry, Creggan all standing together in Creggan last Friday, was something I think was quite unique and quite different."
Ms McKee had written for publications including Private Eye, the Atlantic, Mosaic Science and Mediagazer.
She had also signed a two-book deal with the publisher Faber and Faber, with her forthcoming book The Lost Boys due out in 2020.
The hashtag #IStandWithLyra has been trending on Twitter, which Ms McKee used prolifically.
Comedian Patrick Kielty, who is from Northern Ireland, tweeted: "Today Lyra McKee is laid to rest. She believed in peace, tolerance and equality. The exact opposite of those responsible. They will never win because Lyra will always be the future. And her truth will continue to be told. #IStandWithLyra"
Fellow members of the National Union of Journalists formed a guard of honour at the cathedral.
The union described Ms McKee as "one of the most promising journalists" in Northern Ireland.
There was also a gathering at Guildhall Square in Derry for those who could not attend the funeral.