The announcement, in which Ms Dowie cites a desire to spend more time with family, comes after she was confirmed as Invercargill candidate for National last year and means a new selection process will be needed.
Ms Dowie, who was first elected to Parliament in 2014, took a hit when it was revealed police were investigating a text message, allegedly sent from her phone, to Mr Ross.
The text message, which included the words ''You deserve to die'' was sent in the wake of the end of an extra-marital relationship between the two MPs.
Well-informed sources said the affair had caused turmoil in National party circles in Invercargill.
Police eventually decided she had no case to answer.
In a statement today Ms Dowie said serving the people of Invercargill and wider Southland as MP was "one of my proudest achievements".
"Despite being re-selected as the candidate, I have made the decision not to contest the seat.
"My proudest achievements include taking a leading advocacy role in aquaculture policy and development as part of the Southern Regional Development Strategy, leading the conservation portfolio and policy development as National’s spokesperson for conservation and chairing the Justice Select Committee’s busy legislative agenda including family violence reforms in my first term.
"It has been a privilege to help many Southlanders behind the scenes on personal constituency matters that have made a real difference in their lives.
However, she said she was most proud of her children Christabel and Hunter.
"I went to Parliament when Christabel was four and Hunter was two years old.
"What has become clear is that my children are at a pivotal age and I wish to be 100% present to share in their successes.
“While this was a difficult decision to make, I feel this is the right decision for me and my family.
She said it had been an honour to work along side "some incredibly talented people in National".
"This includes our leader, Simon Bridges who is a tremendous politician and he will make an excellent Prime Minister."
“I want to thank my family, staff and my colleagues both in caucus and across the National Party.
"I especially thank my Invercargill electorate team and my wider Southern National Party 'family' for their unwavering support. You are the backbone of our Party and Members could not achieve all what they do without you.
"I will fulfil my responsibilities as Member of Parliament for Invercargill and campaign for the National Party up until Election Day. The new candidate for Invercargill will have my full support. I wish the National team all the very best in the upcoming election."
Mr Bridges this morning paid tribute to outgoing MPs Ms Dowie, David Carter and Nicky Wagner.
"David Carter, Nicky Wagner and Sarah Dowie have all been fantastic members of our caucus.
"David was one of the most competent and fair Speaker’s we’ve had at Parliament. Nicky was a hardworking Minister who fought for our most vulnerable and Sarah has been a valuable and passionate advocate for conservation in Government and Opposition."
Mr Bridges announced a reshuffle of the roles held by the outgoing MPs, with Jacqui Dean taking on conservation, which was previously held by Ms Dowie.
The National Party Board also decided that Paulo Garcia, who previously ran in New Lynn, would become a list only candidate.
