“I spoke to Arlene today and she informed me of her decision to step down. I wished her and and her family well.
"I have worked alongside Arlene Foster this past year in what has been a difficult and challenging time for everyone with the unexpected onset of the Covid pandemic.
"Throughout the pandemic I acknowledge the efforts Arlene Foster has made as First Minister, and the service that she has given in working with the rest of the Executive as we have battled the biggest health crisis in a generation," she said.
In a statement issues on Wednesday afternoon Mrs. Foster said she would be stepping down as leader of the DUP on May 28 but that she would serve as First Minister until the summer recess.
Mrs. O'Neill said: "It is now a matter for the DUP to choose a replacement.
"The incoming DUP leader should recognise that the political landscape across our island has changed.
"The broad community are impatient for social reform and political change which reflects a modern and progressive society where everyone can feel that they belong on an equal basis.
“As Joint Head of Government my focus, and the focus of our Executive, must remain on the task of leading us safely and sustainably out of the pandemic, building a fairer economy recovery, providing first-class public services and delivering the New Decade, New Approach deal to the benefit of every section of our society.
“This requires a genuine commitment from all political leaders to power-sharing and to work to deliver equality for women, for the LGBT community, for Irish language and identity and all sections of our community."
The Deputy First Minister said she will work with whoever the DUP elect in Mrs. Foster's stead but promised to resist 'regressive' politics.
"Within the Executive and Assembly, Sinn Féin will work with all parties to progress social reform, political change and economic prosperity - but we will robustly oppose damaging policies or regressive throwback politics of the past.
"The public and electorate want the parties to enter into a new era and make politics work in their interests. This is certainly my top priority now and in the time ahead."