In a statement to the press on her blog, she stated she and John Butler, a family friend, were in the early stages of a relationship.
Mr Butler left his wife in December and Mrs Dorries said the nature of their friendship changed over the Christmas period.
The Conservative MP posted the statement on Friday evening (January 7) ahead of the national press breaking the story.
Mrs Dorries, 53 and a mother of two who separated from her first husband in 2006, said: “I can confirm that I am in the early stages of a romantic relationship with John Butler.
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“John and I have been friends for many years and the status of our relationship altered over the Christmas period following his decision to leave his wife.
“We both have the full support of our five teenage and young adult daughters who have been our first consideration throughout.”
In a statement John Butler, 55, said: “Having been in an abusive relationship for a considerable time, I took the decision to leave my wife, Rachael Butler, who suffers from alcoholism, in December 2010.
“I will confirm that I am in a romantic relationship with Nadine Dorries, who has been a good friend for 13 years.
“I have the full support of my two daughters, family and friends who have been incredibly kind with the generosity and care they have shown towards us.
“My decision to leave Rachael was taken separately from that to enter a relationship with Nadine. Had I not known Nadine, I would still have left Rachael.
“I now hope to be able to create a more peaceful stable, family environment for my two daughters from that which they have been used to for some considerable time.”
Nadine Dorries has been MP for Mid Beds since 2005.