Organisers are anticipating at least 5,000 people at a gathering of Christian worshippers in Trafalgar Square on Sunday (June 9).
The event on Pentecost Sunday will mark the culmination of an annual prayer campaign launched by the Archbishops of Canterbury and York, called Thy Kingdom Come 2019.
Last year saw churches from more than 65 denominations in 114 countries taking part in the 10 days of prayer, from Anglicans to Roman Catholics, and Orthodox to Methodists.
This year even larger numbers are expected to take part.
The event, starting at noon, is family-oriented and will have traditional and modern music.
Grammy award-winning singer-songwriter Matt Redman is performing, along with Kingdom Choir, made famous by their outstanding performance at the wedding of the Duke & Duchess of Sussex last year.
Brighton based singer-songwriter Lou Fellingham will also be performing, as well as Sounds of New Wine, winner of Premier Gospel’s Best Newcomer Award.
At 4pm, Christians from churches across London will gather to pray with Archbishops and church leaders, including Bishop of London Sarah Mullally DBE, who said: “This is a wonderful opportunity for Christians to gather together in an iconic part of our great city to worship Christ, to seek his will and to pray for his kingdom to come.
“It was humbling to join the huge numbers that assembled at the cathedral last year.”
The Archbishop of Canterbury, Justin Welby will be there too, along with Cardinal Vincent Nichols, Archbishop Angaelos and Pastor Agu Irukwu.
The Rev Trey Hall, from the Methodist Church, said: “I am honoured to represent the Methodist Church, a major partner of Thy Kingdom Come.
I hope that diverse Christians of every background and belief will join us and invite friends to come along, too.”