Great Yarmouth MP Brandon Lewis has quit his cabinet post saying the values of "honesty, integrity and mutual respect" are no longer being upheld.
It came as the slew of resignations from the government and party reached more than 50 on Thursday morning.
Prime Minister Boris Johnson said he planned to step down, but would stay in post until October.
In his resignation letter Mr Lewis spoke of what he had achieved as Secretary of State for Northern Ireland and outlined the reasons for leaving saying the country "deserved better".
Here's what he said:
It is with regret that I submit my resignation from the Government.
It has been an incredible honour to serve in Government over the last ten years under three Prime Ministers, most recently as Secretary of State for Northern Ireland.
Through the challenges of the last two and a half years, we have taken important steps to secure the future peace and prosperity of Northern Ireland.
I am pleased to have guaranteed the greatest funding settlement for Northern Ireland since devolution in 1998.
The legacy of the Troubles is one of the most complex and sensitive policy issues we have faced, one that successive Governments have struggled to address, so I am immensely proud that we have persevered and brought in the Northern Ireland (Legacy and Reconciliation) Bill.
We have taken huge strides to level up the economy of Northern Ireland and have not shied away from taking other difficult decisions; confronting the practical issues with the Northern Ireland Protocol, advocating for the reproductive rights of women and championing the benefits of integrated education for all.
A decision to leave Government is never taken lightly, particularly at such a critical time for Northern Ireland.
I have taken a lot of time to consider this decision, having outlined my position to you at length last night.
I have served loyally in your Cabinet and you have achieved much during your time as the leader of our Party and as Prime Minister.
I have given you, and those around you, the benefit of the doubt. I have gone out and defended this Government both publicly and privately.
We are, however, now past the point of no return.
I cannot sacrifice my personal integrity to defend things as they stand now.
It is clear that our Party, parliamentary colleagues, volunteers and the whole country, deserve better.
I delivered my first campaign leaflet as a teenager and the Conservative Party has been hugely influential in my life ever since.
In recent weeks and months, we have been relentlessly on the defensive, consumed by introspection and in-fighting.
A divided Party cannot win elections.
It cannot deliver for those who trusted us with their votes for the first time in 2019.
A decent and responsible Government relies on honesty, integrity and mutual respect - it is a matter of profound personal regret for me that I must leave Government as I no longer believe those values are being upheld.
Great Yarmouth MP Brandon Lewis. (Image: PA Wire/PA Images)
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