Brundtland, 57, in a carefully-managed hand-over of power, said that Labour Party leader Thorbjoern Jagland would succeed her as Prime Minister.
Brundtland, known internationally for her strong-minded views, said it was time to make clear who would be at the helm of a Norwegian Labour government beyond this parliamentary election and into the next century.
Brundtland had already said she wanted to step down after dominating Norwegian politics since 1981.
But the timing was a surprise as an announcement was expected at the November convention.
Brundtland has taken a mauling in the traditionally sympathetic Norwegian Press.
She was Prime Minister for eight months in 1981 and again from 1986 to 1989 and again from 1990 until now a total of almost 12 years in office which saw the once-powerful Conservative Party almost wiped off.
A half-page cartoon in the best-selling daily Dagbladet last week depicted the stocky Prime Minister as a bloated monarch surrounded by tired courtiers paying little or no attention to any of her announcements.
Brundtland, who leads a minority government, told Parliament she would submit her resignation to the King.
We are heading for a new parliamentary election and a new four-year legislature, she told Parliament. I feel it is proper that the governments leadership and set-up be clarified well ahead of the election.
In light of this background I have told the King that I will submit my resignation in a cabinet session on Friday, she said.
There has also been speculation that Brundtland may resign well before general elections in September 1997 to seek an office at the United Nations or another internaitonal body.
She will be succeeded as head of the Norwegian Labour government by the incumbent leader of the Norwegian Labour Party, Thorbjoern Jagland, a statement from the Prime Ministers office said.
