'Show Up' aims to get Christians actively engaged in politics through direct participation and prayer.
The campaign book 'Those Who Show Up' was written by Andy Flannagan from the group, discussing faith and politics.
He'll be reading from it outside Westminster, and says the political system directly affects everyone and is a tool to make changes in society.
Speaking before the event he said, "I just hope the weather is good and my voice holds out. Let's pray the gathering will be a powerful reminder that decisions are made by those who show up. Including showing up in prayer."
Mark Scott, from Christians in Politics tells Premier Christians can live authentic and politically-engaged lives at the same time. He said: "Jesus calls us to be the soul and light of the world, and that means not hiding away and not building up a wall between us and various spheres of society, including politics.
"So we feel that 'Show Up' is an important message because it is about being salt and light - and seeing politics as another mission field where we can really shed God's light."
A recent poll by the Evangelical Alliance found 94% of evangelical Christians are "certain" or "likely" to vote in May's election.
'Show Up' created a video to get more Christians more involved in decision-making before the country goes to the polls in May: