Ms McKee was shot dead as she observed clashes between police and New IRA dissidents on the Creggan estate in Londonderry on April 18.
Her family has paid tribute to her as “a best friend and confidante”.
The 29-year-old’s funeral will take place in St Anne’s Cathedral, Belfast, at 1pm on Wednesday, and she will later be laid to rest in Carnmoney cemetery.
Mrs May and Mr Corbyn will miss Prime Minister’s Questions, where they will be replaced by David Liddington and Emily Thornberry respectively.
SNP Westminster leader Ian Blackford will also attend the service.
A tribute from her mother Joan, brothers Gary and David, and sisters Joan Hunter, Nichola Corner and Mary Crossan said: “On Thursday 18th April our beautiful Lyra was taken from us.
“A daughter, a sister, an aunt, a great-aunt, a partner, a niece, a cousin, and above all, a best friend and confidante to so many of us.
“A friend to all, a gentle innocent soul who wouldn’t wish ill on anyone. Such a warm and innocent heart, she was the greatest listener, someone who had time for everyone.”
The McKee family added: “She was a smart, strong-minded woman who believed passionately in inclusivity, justice and truth.
“Lyra spoke to and made friends with anybody and everybody, no matter what their background, those of all political views and those with none. This openness, and her desire to bring people together, made her totally apolitical.”
They said: “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.”
Sara Canning, Ms McKee’s partner, said previously: “Our hopes and dreams and all of her amazing potential was snuffed out by this single barbaric act.”
Ms McKee’s funeral is intended to be a cross-community, cross-border and multi-cultural service, while members of the National Union of Journalists (NUJ) will form a guard of honour.
Various political and community leaders are due to attend, including Taoiseach Leo Varadkar, President of Ireland Michael D Higgins and Irish Minister for Foreign Affairs Simon Coveney.
Those attending were asked to wear Harry Potter and Marvel Comic merchandise in tribute to the journalist’s love of both works.
Miss McKee’s family asked that only family flowers are laid, but a donation can be made via a GoFundMe page set up by the NUJ - https://uk.gofundme.com/in-memory-of-lyra-mckee
The New IRA admitted responsibility for the murder on Tuesday in a statement given to The Irish News.
Using a recognised code word, the group offered “full and sincere apologies” to Ms McKee’s family and friends, claiming: “We have instructed our volunteers to take the utmost care in future when engaging the enemy, and put in place measures to help ensure this.”
The New IRA is an amalgam of armed groups opposed to the peace process and it recently claimed responsibility for parcel bombs sent to London and Glasgow in March.
Police believe the violence was orchestrated in response to an earlier search by officers aimed at averting imminent trouble associated with the week’s anniversary of the Easter Rising.