The Johan Sverdrup field is the fifth largest oil field on the Norwegian continental shelf and is the biggest field development in the region since the 1980s with a resource estimate of between 2.2 and 3.12 billion barrels of oil equivalent.
Phase two development will increase field production from 440,000 barrels of oil per day to 660,000 bopd and follows the first phase development which is 90% complete.
The plan for development was discussed in the Norwegian parliament and the stamp of approval was officially granted overnight.
"Johnan Sverdrup is a world-class field that will provide value to its owners and society for 50 years ahead with record-low emissions," Equinor vice president for Technology, Projects and Drilling Anders Opedal said.
"This truly marks the beginning of the second development phase."
Equinor expects to spend NOK 41 billion (A$6.79 billion) on the development, which includes construction of a new processing platform and modifications to the riser platform as well as five new subsea systems.
Production from phase two is expected to begin in November.
Equinor is the operator of the field with a 40% interest alongside Lundin Norway (22.6%), Petoro (17.36%, Aker BP (11.6%) and Total (8.4%).
The Johan Sverdrup field is powered from shore, placing it among the oil and gas fields with the lowest CO2 emissions in the world.
In the second phase the field will also supply shore power to other nearby fields including the Edvard Grieg, Gina Krog and Ivar Aasen fields.
Equinor has been at pains to communicate its efforts to minimise carbon emissions and environmental responsibility as public attitudes to oil and gas operations continues to slide in Norway.
At its Annual General Meeting yesterday Equinor faced a motion by activist investors to "refrain from fossil fuel exploration and production activities in frontier and immature areas and areas of particularly high ecological value."
The motion received support from Dutch investment bank Aegon, but ultimately was voted down by shareholders.
In March this year, Norway's sovereign wealth fund, which has a total of US$1 trillion in assets around the world built largely on oil money, announced it was moving away from investing in oil and gas upstream exploration.
The fund owns 67% of state oiler Equinor also has US$37 billion worth of investments in supermajors ExxonMobil, BP, Shell and Total.
The move attracted widespread coverage and cheers from pro-environment groups, but in reality only represents $8 billion in smaller investments in large companies like China's CNOOC and smaller oilers and will not affect the majority of its investment.