Associate Health Minister Ruth Dyson has quit after being charged with drunk driving.
The Banks Peninsula MP has released a statement outlining how she was stopped by police last night and failed a breath alcohol test.
Government sources say Ms Dyson's breath alcohol reading was almost twice the legal limit.
She says she recognises her behaviour calls into question her ability to continue to hold her ministerial warrants and has therefore offered Prime Minister Helen Clark her resignation.
Ms Clark says she has accepted Ms Dyson's resignation with extreme regret, saying she has been one of the Government's hardest-working ministers.
The Prime Minister says she still considers Ms Dyson to be an invaluable member of her team, and today's decision does not rule out the possibility that she will be reinstated to ministerial responsibility in the future.
National's health spokesman Wyatt Creech says Ms Dyson should be commended for realising that she had no alternative but to go.
United leader Peter Dunne has applauded the decision to resign, saying he admires Ms Dyson for her decisiveness and courage.
Ms Dyson, aged 43, was associate minister of health, accident insurance, and social services and employment. She also held the disabilities issues portfolio.
Active in women's organisations, the peace movement and environmental groups since the early 1970s, she became an electorate organiser in Westport for Labour in 1981.
In 1985 she moved to Wellington and worked on the Homosexual Law Reform Bill.
Ms Dyson was appointed as adviser to the Minister of Employment in 1986, then as adviser to the Wellington Regional Employment and ACCESS Council.
She entered Parliament in 1993 as MP for Lyttelton, and became a list MP in 1996.
In 1999, she was elected to represent Banks Peninsula.