Around 2,000 guests will be hear from the Bishop of London, Rt Revd Richard Chartres, worship leader Graham Kendrick, who has written a song especially for the occasion, the All Souls Orchestra and the Riding Lights Theatre company.
Speaking ahead of the event Premier's Chief Executive Peter Kerridge said: "It's been a marvellous journey.
"The celebration and thanksgiving service is to mark that and plan for the next few years and what God has in store for us."
In the programme notes, Premier's Acting Chairman Jonathan Alderton Ford said: "It seems such a long time since that sunny day on the 10th June 1995 in Battersea Park, when Premier Christian Radio went on the air for the first time.
"The journey since then has been exciting, full of both challenges and opportunities. But through it all we have been so conscious of the faithfulness of God that has led us to this day. I believe Premier stands on the brink of another amazing 20 years."
The service will be broadcast live at 7pm on Premier Christian Radio.